EVMS User Guide

Christine Lorenz

IBM

Joy Goodreau

IBM

Kylie Smith

IBM

September 16, 2004

Special Notices

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Table of Contents

Preface

1. What is EVMS?

1.1. Why choose EVMS?
1.2. The EVMS user interfaces
1.3. EVMS terminology
1.4. What makes EVMS so flexible?
1.5. Plug-in layer definitions

2. Using the EVMS interfaces

2.1. EVMS GUI
2.2. EVMS Ncurses interface
2.3. EVMS Command Line Interpreter

3. The EVMS log file and error data collection

3.1. About the EVMS log file
3.2. Log file logging levels
3.3. Specifying the logging levels

4. Viewing compatibility volumes after migrating

4.1. Using the EVMS GUI
4.2. Using Ncurses
4.3. Using the CLI

5. Obtaining interface display details

5.1. Using the EVMS GUI
5.2. Using Ncurses
5.3. Using the CLI

6. Adding and removing a segment manager

6.1. When to add a segment manager
6.2. Types of segment managers
6.3. Adding a segment manager to an existing disk
6.4. Adding a segment manager to a new disk
6.5. Example: add a segment manager
6.6. Removing a segment manager
6.7. Example: remove a segment manager

7. Creating segments

7.1. When to create a segment
7.2. Example: create a segment

8. Creating a container

8.1. When to create a container
8.2. Example: create a container

9. Creating regions

9.1. When to create regions
9.2. Example: create a region

10. Creating drive links

10.1. What is drive linking?
10.2. How drive linking is implemented
10.3. Creating a drive link
10.4. Example: create a drive link
10.5. Expanding a drive link
10.6. Shrinking a drive link
10.7. Deleting a drive link

11. Creating snapshots

11.1. What is a snapshot?
11.2. Creating snapshot objects
11.3. Example: create a snapshot
11.4. Reinitializing a snapshot
11.5. Expanding a snapshot
11.6. Deleting a snapshot
11.7. Rolling back a snapshot

12. Creating volumes

12.1. When to create a volume
12.2. Example: create an EVMS native volume
12.3. Example: create a compatibility volume

13. FSIMs and file system operations

13.1. The FSIMs supported by EVMS
13.2. Example: add a file system to a volume
13.3. Example: check a file system

14. Clustering operations

14.1. Rules and restrictions for creating cluster containers
14.2. Example: create a private cluster container
14.3. Example: create a shared cluster container
14.4. Example: convert a private container to a shared container
14.5. Example: convert a shared container to a private container
14.6. Example: deport a private or shared container
14.7. Deleting a cluster container
14.8. Failover and Failback of a private container on Linux-HA
14.9. Remote configuration management
14.10. Forcing a cluster container to be active

15. Converting volumes

15.1. When to convert volumes
15.2. Example: convert compatibility volumes to EVMS volumes
15.3. Example: convert EVMS volumes to compatibility volumes

16. Expanding and shrinking volumes

16.1. Why expand and shrink volumes?
16.2. Example: shrink a volume
16.3. Example: expand a volume

17. Adding features to an existing volume

17.1. Why add features to a volume?
17.2. Example: add drive linking to an existing volume

18. Selectively activating volumes and objects

18.1. Initial activation using /etc/evms.conf
18.2. Activating and deactivating volumes and objects

19. Mounting and unmounting volumes from within EVMS

19.1. Mounting a volume
19.2. Unmounting a volume
19.3. The SWAPFS file system

20. Plug-in operations tasks

20.1. What are plug-in tasks?
20.2. Example: complete a plug-in operations task

21. Deleting objects

21.1. How to delete objects: delete and delete recursive
21.2. Example: perform a delete recursive operation

22. Replacing objects

22.1. What is object-replace?
22.2. Replacing a drive-link child object

23. Moving segment storage objects

23.1. What is segment moving?
23.2. Why move a segment?
23.3. Which segment manager plug-ins implement the move function?
23.4. Example: move a DOS segment

A. The DOS plug-in

A.1. How the DOS plug-in is implemented
A.2. Assigning the DOS plug-in
A.3. Creating DOS partitions
A.4. Expanding DOS partitions
A.5. Shrinking DOS partitions
A.6. Deleting partitions

B. The MD region manager

B.1. Characteristics of Linux RAID levels
B.2. Creating an MD region
B.3. Active and spare objects
B.4. Faulty objects
B.5. Resizing MD regions
B.6. Replacing objects

C. The LVM plug-in

C.1. How LVM is implemented
C.2. Container operations
C.3. Region operations

D. The LVM2 plug-in

D.1. Container operations
D.2. Region operations

E. The CSM plug-in

E.1. Assigning the CSM plug-in
E.2. Unassigning the CSM plug-in
E.3. Deleting a CSM container

F. JFS file system interface module

F.1. Creating JFS file systems
F.2. Checking JFS file systems
F.3. Removing JFS file systems
F.4. Expanding JFS file systems
F.5. Shrinking JFS file systems

G. XFS file system interface module

G.1. Creating XFS file systems
G.2. Checking XFS file systems
G.3. Removing XFS file systems
G.4. Expanding XFS file systems
G.5. Shrinking XFS file systems

H. ReiserFS file system interface module

H.1. Creating ReiserFS file systems
H.2. Checking ReiserFS file systems
H.3. Removing ReiserFS file systems
H.4. Expanding ReiserFS file systems
H.5. Shrinking ReiserFS file systems

I. Ext-2/3 file system interface module

I.1. Creating Ext-2/3 file systems
I.2. Checking Ext-2/3 file systems
I.3. Removing Ext-2/3 file systems
I.4. Expanding and shrinking Ext-2/3 file systems

J. OpenGFS file system interface module

J.1. Creating OpenGFS file systems
J.2. Checking OpenGFS file systems
J.3. Removing OpenGFS file systems
J.4. Expanding and shrinking OpenGFS file systems

K. NTFS file system interface module

K.1. Creating NTFS file systems
K.2. Fixing NTFS file systems
K.3. Cloning NTFS file systems
K.4. Removing NTFS file systems
K.5. Expanding and shrinking NTFS file systems

List of Tables
1. Organization of the EVMS User Guide
1-1. EVMS user interfaces
2-1. Accelerator keys in the Main Window
2-2. Accelerator keys in the views
2-3. Accelerator keys in the selection window
2-4. Accelerator keys in the configuration options window
2-5. Widget navigation keys in the configuration options window
3-1. EVMS logging levels
16-1. FSIM support for expand and shrink operations

List of Figures
4-1. GUI start-up window
4-2. Ncurses start-up window
4-3. CLI volume query results

List of Examples
6-1. Add the DOS Segment Manager
6-2. Remove the DOS Segment Manager
7-1. Create a 100MB segment
8-1. Create "Sample Container"
9-1. Create "Sample Region"
10-1. Create a drive link
11-1. Create a snapshot of a volume
12-1. Create an EVMS native volume
12-2. Create a compatibility volume
13-1. Add a JFS File System to a Volume
13-2. Check a JFS File System
14-1. Create a private cluster container
14-2. Create a shared cluster container
14-3. Convert a private container to shared
14-4. Convert a shared container to private
14-5. Deport a cluster container
15-1. Convert a compatibility volume
15-2. Convert an EVMS volume
16-1. Shrink a volume
16-2. Expand a volume
17-1. Add drive linking to an existing volume
20-1. Add a spare disk to a compatibility volume made from an MDRaid5 region
21-1. Destroy a volume and the region and container below it

Preface

This guide tells how to configure and manage Enterprise Volume Management System (EVMS). EVMS is a storage management program that provides a single framework for managing and administering your system's storage.

This guide is intended for Linux system administrators and users who are responsible for setting up and maintaining EVMS.

For additional information about EVMS or to ask questions specific to your distribution, refer to the EVMS mailing lists. You can view the list archives or subscribe to the lists from the EVMS Project web site.

The following table shows how this guide is organized:

Table 1. Organization of the EVMS User Guide

Chapter or appendix title	Contents
1. What is EVMS?	Discusses general EVMS concepts and terms.
2. Using the EVMS interfaces	Describes the three EVMS user interfaces and how to use them.
3. The EVMS log file and error data collection	Discusses the EVMS information and error log file and explains how to change the logging level.
4. Viewing compatibility volumes after migrating	Tells how to view existing files that have been migrated to EVMS.
5. Obtaining interface display details	Tells how to view detailed information about EVMS objects.
6. Adding and removing a segment manager	Discusses segments and explains how to add and remove a segment manager.
7. Creating segments	Explains when and how to create segments.
8. Creating containers	Discusses containers and explains when and how to create them.
9. Creating regions	Discusses regions and explains when and how to create them.
10. Creating drive links	Discusses the drive linking feature and tells how to create a drive link.
11. Creating snapshots	Discusses snapshotting and tells how to create a snapshot.
12. Creating volumes	Explains when and how to create volumes.
13. FSIMs and file system operations	Discusses the standard FSIMs shipped with EVMS and provides examples of adding file systems and coordinating file checks with the FSIMs.
14. Clustering operations	Describes EVMS clustering and how to create private and shared containers.
15. Converting volumes	Explains how to convert EVMS native volumes to compatibility volumes and compatibility volumes to EVMS native volumes.
16. Expanding and shrinking volumes	Tells how to expand and shrink EVMS volumes with the various EVMS user interfaces.
17. Adding features to an existing volume	Tells how to add additional features, such as drive linking, to an existing volume.
18. Selectively activating volumes and objects	Explains how to selectively activate and deactive volumes and options.
19. Mounting and unmounting volumes from within EVMS.	Tells how to have EVMS mount and unmount volumes so you do not have to open a separate terminal session.
20. Plug-in operations tasks	Discusses the plug-in tasks that are available within the context of a particular plug-in.
21. Deleting objects	Tells how to safely delete EVMS objects.
22. Replacing objects	Tells how to change the configuration of a volume or storage object.
23. Moving segment storage objects	Discusses how to use the move function for moving segments.
A. The DOS plug-in	Provides details about the DOS plug-in, which is a segment manager plug-in.
B. The MD region manager	Explains the Multiple Disks (MD) support in Linux that is a software implementation of RAID.
C. The LVM plug-in	Tells how the LVM plug-in is implemented and how to perform container operations.
D. The LVM2 plug-in	Tells how the LVM2 plug-in is implemented and how to perform container operations on LVM2 containers.
E. The CSM plug-in	Explains how the Cluster Segment Manager (CSM) plug-in is implemented and how to perform CSM operations.
F. JFS file system interface module	Provides information about the JFS FSIM.
G. XFS file system interface module	Provides information about the XFS FSIM.
H. ReiserFS file system interface module	Provides information about the ReiserFS FSIM.
I. Ext-2/3 file system interface module	Provides information about the Ext-2/3 FSIM.
J. OpenGFS file system interface module	Provides information about the OpenGFS FSIM.
K. NTFS file system interface module	Provides information about the NTFS FSIM.

Chapter 1. What is EVMS?

EVMS brings a new model of volume management to Linux�. EVMS integrates all aspects of volume management, such as disk partitioning, Linux logical volume manager (LVM) and multi-disk (MD) management, and file system operations into a single cohesive package. With EVMS, various volume management technologies are accessible through one interface, and new technologies can be added as plug-ins as they are developed.

1.1. Why choose EVMS?

EVMS lets you manage storage space in a way that is more intuitive and flexible than many other Linux volume management systems. Practical tasks, such as migrating disks or adding new disks to your Linux system, become more manageable with EVMS because EVMS can recognize and read from different volume types and file systems. EVMS provides additional safety controls by not allowing commands that are unsafe. These controls help maintain the integrity of the data stored on the system.

You can use EVMS to create and manage data storage. With EVMS, you can use multiple volume management technologies under one framework while ensuring your system still interacts correctly with stored data. With EVMS, you are can use drive linking, shrink and expand volumes, create snapshots of your volumes, and set up RAID (redundant array of independent devices) features for your system. You can also use many types of file systems and manipulate these storage pieces in ways that best meet the needs of your particular work environment.

EVMS also provides the capability to manage data on storage that is physically shared by nodes in a cluster. This shared storage allows data to be highly available from different nodes in the cluster.

1.2. The EVMS user interfaces

There are currently three user interfaces available for EVMS: graphical (GUI), text mode (Ncurses), and the Command Line Interpreter (CLI). Additionally, you can use the EVMS Application Programming Interface to implement your own customized user interface.

Table 1-1 tells more about each of the EVMS user interfaces.

Table 1-1. EVMS user interfaces

User interface	Typical user	Types of use	Function
GUI	All	All uses except automation	Allows you to choose from available options only, instead of having to sort through all the options, including ones that are not available at that point in the process.
Ncurses	Users who don't have GTK libraries or X Window Systems on their machines	All uses except automation	Allows you to choose from available options only, instead of having to sort through all the options, including ones that are not available at that point in the process.
Command Line	Expert	All uses	Allows easy automation of tasks

1.3. EVMS terminology

To avoid confusion with other terms that describe volume management in general, EVMS uses a specific set of terms. These terms are listed, from most fundamental to most comprehensive, as follows:

Logical disk

Representation of anything EVMS can access as a physical disk. In EVMS, physical disks are logical disks.

Sector

The lowest level of addressability on a block device. This definition is in keeping with the standard meaning found in other management systems.

Disk segment

An ordered set of physically contiguous sectors residing on the same storage object. The general analogy for a segment is to a traditional disk partition, such as DOS or OS/2 �

Storage region

An ordered set of logically contiguous sectors that are not necessarily physically contiguous.

Storage object

Any persistent memory structure in EVMS that can be used to build objects or create a volume. Storage object is a generic term for disks, segments, regions, and feature objects.

Storage container

A collection of storage objects. A storage container consumes one set of storage objects and produces new storage objects. One common subset of storage containers is volume groups, such as AIX� or LVM.

Storage containers can be either of type private or cluster.

Cluster storage container

Specialized storage containers that consume only disk objects that are physically accessible from all nodes of a cluster.

Private storage container: A collection of disks that are physically accessible from all nodes of a cluster, managed as a single pool of storage, and owned and accessed by a single node of the cluster at any given time.
Shared storage container: A collection of disks that are physically accessible from all nodes of a cluster, managed as a single pool of storage, and owned and accessed by all nodes of the cluster simultaneously.
Deported storage container: A shared cluster container that is not owned by any node of the cluster.

Feature object

A storage object that contains an EVMS native feature.

An EVMS Native Feature is a function of volume management designed and implemented by EVMS. These features are not intended to be backward compatible with other volume management technologies.

Logical volume

A volume that consumes a storage object and exports something mountable. There are two varieties of logical volumes: EVMS Volumes and Compatibility volumes.

EVMS Volumes contain EVMS native metadata and can support all EVMS features. /dev/evms/my_volume would be an example of an EVMS Volume.

Compatibility volumes do not contain any EVMS native metadata. Compatibility volumes are backward compatible to their particular scheme, but they cannot support EVMS features. /dev/evms/md/md0 would be an example of a compatibility volume.

1.4. What makes EVMS so flexible?

There are numerous drivers in the Linux kernel, such as Device Mapper and MD (software RAID), that implement volume management schemes. EVMS is built on top of these drivers to provide one framework for combining and accessing the capabilities.

The EVMS Engine handles the creation, configuration, and management of volumes, segments, and disks. The EVMS Engine is a programmatic interface to the EVMS system. User interfaces and programs that use EVMS must go through the Engine.

EVMS provides the capacity for plug-in modules to the Engine that allow EVMS to perform specialized tasks without altering the core code. These plug-in modules allow EVMS to be more extensible and customizable than other volume management systems.

1.5. Plug-in layer definitions

EVMS defines a layered architecture where plug-ins in each layer create abstractions of the layer or layers below. EVMS also allows most plug-ins to create abstractions of objects within the same layer. The following list defines these layers from the bottom up.

Device managers

The first (bottom) layer consists of device managers. These plug-ins communicate with hardware device drivers to create the first EVMS objects. Currently, all devices are handled by a single plug-in. Future releases of EVMS might need additional device managers for network device management (for example, to manage disks on a storage area network (SAN)).

Segment managers

The second layer consists of segment managers. These plug-ins handle the segmenting, or partitioning, of disk drives. The Engine components can replace partitioning programs, such as fdisk and Disk Druid, and EVMS uses Device Mapper to replace the in-kernel disk partitioning code. Segment managers can also be "stacked," meaning that one segment manager can take as input the output from another segment manager.

EVMS provides the following segment managers: DOS, GPT, System/390� (S/390), Cluster, BSD, Mac, and BBR. Other segment manager plug-ins can be added to support other partitioning schemes.

Region managers

The third layer consists of region managers. This layer provides a place for plug-ins that ensure compatibility with existing volume management schemes in Linux and other operating systems. Region managers are intended to model systems that provide a logical abstraction above disks or partitions.

Like segment managers, region managers can also be stacked. Therefore, the input object(s) to a region manager can be disks, segments, or other regions.

There are currently three region manager plug-ins in EVMS: Linux LVM, LVM2, and Multi-Disk (MD).

Linux LVM: The Linux LVM plug-in provides compatibility with the Linux LVM and allows the creation of volume groups (known in EVMS as containers) and logical volumes (known in EVMS as regions).
LVM2: The LVM2 plug-in provides compatibility with the new volume format introduced by the LVM2 tools from Red Hat. This plug-in is very similar in functionality to the LVM plug-in. The primary difference is the new, improved metadata format.
MD: The Multi-Disk (MD) plug-in for RAID provides RAID levels linear, 0, 1, 4, and 5 in software. MD is one plug-in that displays as four region managers that you can choose from.

EVMS features

The next layer consists of EVMS features. This layer is where new EVMS-native functionality is implemented. EVMS features can be built on any object in the system, including disks, segments, regions, or other feature objects. All EVMS features share a common type of metadata, which makes discovery of feature objects much more efficient, and recovery of broken features objects much more reliable. There are three features currently available in EVMS: drive linking, Bad Block Relocation, and snapshotting.

Drive Linking: Drive linking allows any number of objects to be linearly concatenated together into a single object. A drive linked volume can be expanded by adding another storage object to the end or shrunk by removing the last object.
Bad Block Relocation: Bad Block Relocation (BBR) monitors its I/O path and detects write failures (which can be caused by a damaged disk). In the event of such a failure, the data from that request is stored in a new location. BBR keeps track of this remapping. Additional I/Os to that location are redirected to the new location.
Snapshotting: The Snapshotting feature provides a mechanism for creating a "frozen" copy of a volume at a single instant in time, without having to take that volume off-line. This is useful for performing backups on a live system. Snapshots work with any volume (EVMS or compatibility), and can use any other available object as a backing store. After a snapshot is created and made into an EVMS volume, writes to the "original" volume cause the original contents of that location to be copied to the snapshot's storage object. Reads to the snapshot volume look like they come from the original at the time the snapshot was created.

File System Interface Modules

File System Interface Modules (FSIMs) provide coordination with the file systems during certain volume management operations. For instance, when expanding or shrinking a volume, the file system must also be expanded or shrunk to the appropriate size. Ordering in this example is also important; a file system cannot be expanded before the volume, and a volume cannot be shrunk before the file system. The FSIMs allow EVMS to ensure this coordination and ordering.

FSIMs also perform file system operations from one of the EVMS user interfaces. For instance, a user can make new file systems and check existing file systems by interacting with the FSIM.

Cluster Manager Interface Modules

Cluster Manager Interface Modules, also known as the EVMS Clustered Engine (ECE), interface with the local cluster manager installed on the system. The ECE provides a standardized ECE API to the Engine while hiding cluster manager details from the Engine.

Chapter 2. Using the EVMS interfaces

This chapter explains how to use the EVMS GUI, Ncurses, and CLI interfaces. This chapter also includes information about basic navigation and commands available through the CLI.

2.1. EVMS GUI

The EVMS GUI is a flexible and easy-to-use interface for administering volumes and storage objects. Many users find the EVMS GUI easy to use because it displays which storage objects, actions, and plug-ins are acceptable for a particular task.

2.1.1. Using context sensitive and action menus

The EVMS GUI lets you accomplish most tasks in one of two ways: context sensitive menus or the Actions menu.

Context sensitive menus are available from any of the main "views." Each view corresponds to a page in a notebook widget located on the EVMS GUI main window. These views are made up of different trees or lists that visually represent the organization of different object types, including volumes, feature objects, regions, containers, segments, or disks.

You can view the context sensitive menu for an object by right-clicking on that object. The actions that are available for that object display on the screen. The GUI will only present actions that are acceptable for the selected object at that point in the process. These actions are not always a complete set.

To use the Actions menu, choose Action-><the action you want to accomplish>-><options>. The Actions menu provides a more guided path for completing a task than do context sensitive menus. The Actions option is similar to the wizard or druid approach used by many GUI applications.

All of the operations you need to perform as an administrator are available through the Actions menu.

2.1.2. Saving changes

All of the changes that you make while in the EVMS GUI are only in memory until you save the changes. In order to make your changes permanent, you must save all changes before exiting. If you forget to save the changes and decide to exit or close the EVMS GUI, you are reminded to save any pending changes.

To explicitly save all the changes you made, select Action->Save, and click the Save button.

2.1.3. Refreshing changes

The Refresh button updates the view and allows you to see changes, like mount points, that might have changed outside of the GUI.

2.1.4. Using the GUI "+"

Along the left hand side of the panel views in the GUI is a "+" that resides beside each item. When you click the "+," the objects that are included in the item are displayed. If any of the objects that display also have a "+" beside them, you can expand them further by clicking on the "+" next to each object name.

2.1.5. Using the accelerator keys

You can avoid using a mouse for navigating the EVMS GUI by using a series of key strokes, or "accelerator keys," instead. The following sections tell how to use accelerator keys in the EVMS Main Window, the Selection Window, and the Configuration Options Window.

2.1.5.1. Main Window accelerator keys

In the Main Window view, use the following keys to navigate:

Table 2-1. Accelerator keys in the Main Window

Left and right arrow keys	Navigate between the notebook tabs of the different views.
Down arrow and Spacebar	Bring keyboard focus into the view.

While in a view, use the following keys to navigate:

Table 2-2. Accelerator keys in the views

up and down arrows	Allow movement around the window.
"+"	Opens an object tree.
"-"	Collapses an object tree.
ENTER	Brings up the context menu (on a row).
Arrows	Navigate a context menu.
ENTER	Activates an item.
ESC	Dismisses the context menu.
Tab	Gets you out of the view and moves you back up to the notebook tab.

To access the action bar menu, press Alt and then the underlined accelerator key for the menu choice (for example, "A" for the Actions dropdown menu).

In a dropdown menu, you can use the up and down arrows to navigate. You could also just type the accelerator key for the menu item, which is the character with the underscore. For example, to initiate a command to delete a container, type Alt + "A" + "D" + "C."

Ctrl-S is a shortcut to initiate saving changes. Ctrl-Q is a shortcut to initiate quitting the EVMS GUI.

2.1.5.2. Accelerator keys in the selection window

A selection window typically contains a selection list, plus four to five buttons below it. Use the following keys to navigate in the selection window:

Table 2-3. Accelerator keys in the selection window

Tab	Navigates (changes keyboard focus) between the list and the buttons.
Up and down arrows	Navigates within the selection list.
Spacebar	Selects and deselects items in the selection list.
Enter on the button or type the accelerator character (if one exists)	Activates a button

2.1.5.3. Configuration options window accelerator keys

Use the following keys to navigate in the configuration options window:

Table 2-4. Accelerator keys in the configuration options window

Tab	Cycles focus between fields and buttons
Left and right arrows	Navigate the folder tabs if the window has a widget notebook.
Spacebar or the down arrow	Switches focus to a different notebook page.
Enter or type the accelerator character (if one exists)	Activates a button

For widgets, use the following keys to navigate:

Table 2-5. Widget navigation keys in the configuration options window

Tab	Cycles forward through a set of widgets
Shift-Tab	Cycles backward through a set of widgets.

The widget navigation, selection, and activation is the same in all dialog windows.

2.2. EVMS Ncurses interface

The EVMS Ncurses (evmsn) user interface is a menu-driven interface with characteristics similar to those of the EVMS GUI. Like the EVMS GUI, evmsn can accommodate new plug-ins and features without requiring any code changes.

The EVMS Ncurses user interface allows you to manage volumes on systems that do not have the X and GTK+ libraries that are required by the EVMS GUI.

2.2.1. Navigating through EVMS Ncurses

The EVMS Ncurses user interface initially displays a list of logical volumes similar to the logical volumes view in the EVMS GUI. Ncurses also provides a menu bar similar to the menu bar in the EVMS GUI.

A general guide to navigating through the layout of the Ncurses window is listed below:

Tab cycles you through the available views.
Status messages and tips are displayed on the last line of the screen.
Typing the accelerator character (the letter highlighted in red) for any menu item activates that item. For example, typing A in any view brings down the Actions menu.
Typing A + Q in a view quits the application.
Typing A + S in a view saves changes made during an evmsn session.
Use the up and down arrows to highlight an object in a view. Pressing Enter while an object in a view is highlighted presents a context popup menu.
Dismiss a context popup menu by pressing Esc or by selecting a menu item with the up and down arrows and pressing Enter to activate the menu item.

Dialog windows are similar in design to the EVMS GUI dialogs, which allow a user to navigate forward and backward through a series of dialogs using Next and Previous. A general guide to dialog windows is listed below:

Tab cycles you through the available buttons. Note that some buttons might not be available until a valid selection is made.
The left and right arrows can also be used to move to an available button.
Navigate a selection list with the up and down arrows.
Toggle the selection of an item in a list with spacebar.
Activate a button that has the current focus with Enter. If the button has an accelerator character (highlighted in red), you can also activate the button by typing the accelerator character regardless of whether the button has the current focus.

The EVMS Ncurses user interface, like the EVMS GUI, provides context menus for actions that are available only to the selected object in a view. Ncurses also provides context menus for items that are available from the Actions menu. These context menus present a list of commands available for a certain object.

2.2.2. Saving changes

All changes you make while in the EVMS Ncurses are only in memory until you save the changes. In order to make the changes permanent, save all changes before exiting. If you forget to save the changes and decide to exit the EVMS Ncurses interface, you will be reminded of the unsaved changes and be given the chance to save or discard the changes before exiting.

To explicitly save all changes, press A + S and confirm that you want to save changes.

2.3. EVMS Command Line Interpreter

The EVMS Command Line Interpreter (EVMS CLI) provides a command-driven user interface for EVMS. The EVMS CLI helps automate volume management tasks and provides an interactive mode in situations where the EVMS GUI is not available.

Because the EVMS CLI is an interpreter, it operates differently than command line utilities for the operating system. The options you specify on the EVMS CLI command line to invoke the EVMS CLI control how the EVMS CLI operates. For example, the command line options tell the CLI where to go for commands to interpret and how often the EVMS CLI must save changes to disk. When invoked, the EVMS CLI prompts for commands.

The volume management commands the EVMS CLI understands are specified in the /usr/src/evms-2.2.0/engine2/ui/cli/grammar.ps file that accompanies the EVMS package. These commands are described in detail in the EVMS man page, and help on these commands is available from within the EVMS CLI.

2.3.1. Using the EVMS CLI

Use the evms command to start the EVMS CLI. If you do not enter an option with evms, the EVMS CLI starts in interactive mode. In interactive mode, the EVMS CLI prompts you for commands. The result of each command is immediately saved to disk. The EVMS CLI exits when you type exit. You can modify this behavior by using the following options with evms:

-b

This option indicates that you are running in batch mode and anytime there is a prompt for input from the user, the default value is accepted automatically. This is the default behavior with the -f option.

-c

This option saves changes to disk only when EVMS CLI exits, not after each command.

-f filename

This option tells the EVMS CLI to use filename as the source of commands. The EVMS CLI exits when it reaches the end of filename.

-p

This option only parses commands; it does not execute them. When combined with the -f option, the -p option detects syntax errors in command files.

-h

This option displays help information for options used with the evms command.

-rl

This option tells the CLI that all remaining items on the command line are replacement parameters for use with EVMS commands.

NOTE

Replacement parameters are accessed in EVMS commands using the $(x) notation, where x is the number identifying which replacement parameter to use. Replacement parameters are assigned numbers (starting with 1) as they are encountered on the command line. Substitutions are not made within comments or quoted strings.

An example would be:

evms -c -f testcase -rl sda sdb

sda is the replacement for parameter1 and sdb is the replacement for parameter2

	NOTE
	Information on less commonly used options is available in the EVMS man page.

2.3.2. Notes on commands and command files

The EVMS CLI allows multiple commands to be displayed on a command line. When you specify multiple commands on a single command line, separate the commands with a colon ( : ). This is important for command files because the EVMS CLI sees a command file as a single long command line. The EVMS CLI has no concept of lines in the file and ignores spaces. These features allow a command in a command file to span several lines and use whatever indentation or margins that are convenient. The only requirement is that the command separator (the colon) be present between commands.

The EVMS CLI ignores spaces unless they occur within quote marks. Place in quotation marks a name that contains spaces or other non-printable or control characters. If the name contains a quotation mark as part of the name, the quotation mark must be "doubled," as shown in the following example:

"This is a name containing ""embedded"" quote marks."

EVMS CLI keywords are not case sensitive, but EVMS names are case sensitive. Sizes can be input in any units with a unit label, such as KB, MB, GB, or TB.

Finally, C programming language style comments are supported by the EVMS CLI. Comments can begin and end anywhere except within a quoted string, as shown in the following example:

/* This is a comment */
Create:Vo/*This is a silly place for a comment, but it is
allowed.*/lume,"lvm/Sample Container/My LVM
Volume",compatibility

Chapter 3. The EVMS log file and error data collection

This chapter discusses the EVMS information and error log file and the various logging levels. It also explains how to change the logging level.

3.1. About the EVMS log file

The EVMS Engine creates a log file called /var/log/evmsEngine.log every time the Engine is opened. The Engine also saves copies of up to nine previous Engine sessions in the files /var/log/evmsEngine.n.log, where n is the number of the session between 1 and 9.

3.2. Log file logging levels

There are several possible logging levels that you can choose to be collected in /var/log/evmsEngine.log. The "lowest" logging level, critical, collects only messages about serious system problems, whereas the "highest" level, everything, collects all logging related messages. When you specify a particular logging level, the Engine collects messages for that level and all the levels below it.

The following table lists the allowable log levels and the information they provide:

Table 3-1. EVMS logging levels

Level name	Description
Critical	The health of the system or the Engine is in jeopardy; for example, an operation has failed because there is not enough memory.
Serious	An operation did not succeed.
Error	The user has caused an error. The error messages are provided to help the user correct the problem.
Warning	An error has occurred that the system might or might not be able to work around.
Default	An error has occurred that the system has already worked around.
Details	Detailed information about the system.
Entry_Exit	Traces the entries and exits of functions.
Debug	Information that helps the user debug a problem.
Extra	More information that helps the user debug a problem than the "Debug" level provides.
Everything	Verbose output.

3.3. Specifying the logging levels

By default, when any of the EVMS interfaces is opened, the Engine logs the Default level of messages into the /var/log/evmsEngine.log file. However, if your system is having problems and you want to see more of what is happening, you can change the logging level to be higher; if you want fewer logging messages, you can change the logging level to be lower. To change the logging level, specify the -d parameter and the log level on the interface open call. The following examples show how to open the various interfaces with the highest logging level (everything):

GUI:		evmsgui -d everything

Ncurses:	evmsn -d everything

CLI:		evms -d everything

	NOTE
	If you use the EVMS mailing list for help with a problem, providing to us the log file that is created when you open one of the interfaces (as shown in the previous commands) makes it easier for us to help you.

The EVMS GUI lets you change the logging level during an Engine session. To do so, follow these steps:

Select Settings->Log Level->Engine.
Click the Level you want.

The CLI command, probe, opens and closes the Engine, which causes a new log to start. The log that existed before the probe command was issued is renamed /var/log/evmsEngine.1.log and the new log is named /var/log/evmsEngine.log.

If you will be frequently using a different log level than the default, you can specify the default logging level in /etc/evms.conf rather than having to use the -d option when starting the user interface. The "debug_level" option in the "engine" section sets the default logging level for when the Engine is opened. Using the -d option during the command invocation overrides the setting in /etc/evms.conf.

Chapter 4. Viewing compatibility volumes after migrating

Migrating to EVMS allows you to have the flexibility of EVMS without losing the integrity of your existing data. EVMS discovers existing volume management volumes as compatibility volumes. After you have installed EVMS, you can view your existing volumes with the interface of your choice.

4.1. Using the EVMS GUI

If you are using the EVMS GUI as your preferred interface, you can view your migrated volumes by typing evmsgui at the command prompt. The following window opens, listing your migrated volumes.

Figure 4-1. GUI start-up window

4.2. Using Ncurses

If you are using the Ncurses interface, you can view your migrated volumes by typing evmsn at the command prompt. The following window opens, listing your migrated volumes.

Figure 4-2. Ncurses start-up window

4.3. Using the CLI

If you are using the Command Line Interpreter (CLI) interface, you can view your migrated volumes by following these steps:

Start the Command Line Interpreter by typing evms at the command line.
Query the volumes by typing the following at the EVMS prompt:
query:volumes
Your migrated volumes are displayed as results of the query.

Figure 4-3. CLI volume query results

Chapter 5. Obtaining interface display details

The EVMS interfaces let you view more detailed information about an EVMS object than what is readily available from the main views of the EVMS user interfaces. The type and extent of additional information available is dependent on the interface you use. For example, the EVMS GUI provides more in-depth information than does the CLI.

The following sections show how to find detailed information on the region lvm/Sample Container/Sample Region, which is part of volume /dev/evms/Sample Volume (created in section 10.2).

5.1. Using the EVMS GUI

With the EVMS GUI, it is only possible to display additional details on an object through the Context Sensitive Menus, as shown in the following steps:

Looking at the volumes view, click the "+" next to volume /dev/evms/Sample Volume. Alternatively, look at the regions view.
Right click lvm/Sample Container/Sample Region.
Point at Display Details... and click. A new window opens with additional information about the selected region.
Click More by the Logical Extents box. Another window opens that displays the mappings of logical extents to physical extents.

5.2. Using Ncurses

Follow these steps to display additional details on an object with Ncurses:

Press Tab to reach the Storage Regions view.
Scroll down using the down arrow until lvm/Sample Container/Sample Region is highlighted.
Press Enter.
In the context menu, scroll down using the down arrow to highlight "Display Details..."
Press Enter to activate the menu item.
In the Detailed Information dialog, use the down arrow to highlight the "Logical Extents" item and then use spacebar to open another window that displays the mappings of logical extents to physical extents.

5.3. Using the CLI

Use the query command (abbreviated q) with filters to display details about EVMS objects. There are two filters that are especially helpful for navigating within the command line: list options (abbreviated lo) and extended info (abbreviated ei).

The list options command tells you what can currently be done and what options you can specify. To use this command, first build a traditional query command starting with the command name query, followed by a colon (:), and then the type of object you want to query (for example, volumes, objects, plug-ins). Then, you can use filters to narrow the search to only the area you are interested in. For example, to determine the acceptable actions at the current time on lvm/Sample Container/Sample Region, enter the following command:

query: regions, region="lvm/Sample Container/Sample Region", list options

The extended info filter is the equivalent of Display Details in the EVMS GUI and Ncurses interfaces. The command takes the following form: query, followed by a colon (:), the filter (extended info), a comma (,), and the object you want more information about. The command returns a list containing the field names, titles, descriptions and values for each field defined for the object. For example, to obtain details on lvm/Sample Container/Sample Region, enter the following command:

query: extended info, "lvm/Sample Container/Sample Region"

Many of the field names that are returned by the extended info filter can be expanded further by specifying the field name or names at the end of the command, separated by commas. For example, if you wanted additional information about logical extents, the query would look like the following:

query: extended info, "lvm/Sample Container/Sample Region", Extents

Chapter 6. Adding and removing a segment manager

This chapter discusses when to use a segment manager, what the different types of segment managers are, how to add a segment manager to a disk, and how to remove a segment manager.

6.1. When to add a segment manager

Adding a segment manager to a disk allows the disk to be subdivided into smaller storage objects called disk segments. The add command causes a segment manager to create appropriate metadata and expose freespace that the segment manager finds on the disk. You need to add segment managers when you have a new disk or when you are switching from one partitioning scheme to another.

EVMS displays disk segments as the following types:

Data: a set of contiguous sectors that has been allocated from a disk and can be used to construct a volume or object.
Freespace: a set of contiguous sectors that are unallocated or not in use. Freespace can be used to create a segment.
Metadata: a set of contiguous sectors that contain information needed by the segment manager.

6.2. Types of segment managers

There are seven types of segment managers in EVMS: DOS, GPT, S/390, Cluster, BSD, MAC, and BBR.

6.2.1. DOS Segment Manager

The most commonly used segment manager is the DOS Segment Manager. This plug-in provides support for traditional DOS disk partitioning. The DOS Segment Manager also recognizes and supports the following variations of the DOS partitioning scheme:

OS/2: an OS/2 disk has additional metadata sectors that contain information needed to reconstruct disk segments.
Embedded partitions: support for BSD, SolarisX86, and UnixWare is sometimes found embedded in primary DOS partitions. The DOS Segment Manager recognizes and supports these slices as disk segments.

6.2.2. GUID Partitioning Table (GPT) Segment Manager

The GUID Partitioning Table (GPT) Segment Manager handles the new GPT partitioning scheme on IA-64 machines. The Intel Extensible Firmware Interface Specification requires that firmware be able to discover partitions and produce logical devices that correspond to disk partitions. The partitioning scheme described in the specification is called GPT due to the extensive use of Globally Unique Identifier (GUID) tagging. GUID is a 128 bit long identifier, also referred to as a Universally Unique Identifier (UUID). As described in the Intel Wired For Management Baseline Specification, a GUID is a combination of time and space fields that produce an identifier that is unique across an entire UUID space. These identifiers are used extensively on GPT partitioned disks for tagging entire disks and individual partitions. GPT partitioned disks serve several functions, such as:

keeping a primary and backup copy of metadata
replacing msdos partition nesting by allowing many partitions
using 64 bit logical block addressing
tagging partitions and disks with GUID descriptors

The GPT Segment Manager scales better to large disks. It provides more redundancy with added reliability and uses unique names. However, the GPT Segment Manager is not compatible with DOS, OS/2, or Windows�.

6.2.3. S/390 Segment Manager

The S/390 Segment Manager is used exclusively on System/390 mainframes. The S/390 Segment Manager has the ability to recognize various disk layouts found on an S/390 machine, and provide disk segment support for this architecture. The two most common disk layouts are Linux Disk Layout (LDL) and Common Disk Layout (CDL).

The principle difference between LDL and CDL is that an LDL disk cannot be further subdivided. An LDL disk will produce a single metadata disk segment and a single data disk segment. There is no freespace on an LDL disk, and you cannot delete or re-size the data segment. A CDL disk can be subdivided into multiple data disk segments because it contains metadata that is missing from an LDL disk, specifically the Volume Table of Contents (vtoc) information.

The S/390 Segment Manager is the only segment manager plug-in capable of understanding the unique S/390 disk layouts. The S/390 Segment Manager cannot be added or removed from a disk.

6.2.4. Cluster segment manager

The cluster segment manager (CSM) supports high availability clusters. When the CSM is added to a shared storage disk, it writes metadata on the disk that:

provides a unique disk ID (guid)
names the EVMS container the disk will reside within
specifies the cluster node (nodeid) that owns the disk
specifies the cluster (clusterid)

This metadata allows the CSM to build containers for supporting failover situations. It does so by constructing an EVMS container object that consumes all shared disks discovered by the CSM and belonging to the same container. These shared storage disks are consumed by the container and a single data segment is produced by the container for each consumed disk. A failover of the EVMS resource is accomplished by simply reassigning the CSM container to the standby cluster node and having that node re-run its discovery process.

Adding disks to CSM containers implies that only disk storage objects are acceptable to the CSM. This is an important aspect of the CSM. Other segment managers can be embedded within storage objects and used to further subdivide them. However, the CSM cannot add any other kind of storage object to a CSM container because the container is meant to be a disk group and the entire disk group is reassigned during a failover. So, the CSM only accepts disks when constructing containers. This is important to remember when adding the CSM to a disk. If you choose Add and the CSM does not appear in the list of selectable plug-ins when you know you have a disk, you should look at the Volume list and see if the disk has already been listed as a compatibility volume. If you simply delete the volume, the disk will become an available object and the CSM will then appear in the list of plug-ins because it now has an available disk that it can add to a container.

6.2.5. BSD segment manager

BSD refers to the Berkeley Software Distribution UNIX� operating system. The EVMS BSD segment manager is responsible for recognizing and producing EVMS segment storage objects that map BSD partitions. A BSD disk may have a slice table in the very first sector on the disk for compatibility purposes with other operating systems. For example, a DOS slice table might be found in the usual MBR sector. The BSD disk would then be found within a disk slice that is located using the compatibility slice table. However, BSD has no need for the slice table and can fully dedicate the disk to itself by placing the disk label in the very first sector. This is called a "fully dedicated disk" because BSD uses the entire disk and does not provide a compatibility slice table. The BSD segment manager recognizes such "fully dedicated disks" and provides mappings for the BSD partitions.

6.2.6. MAC segment manager

Apple-partitioned disks use a disk label that is recognized by the MAC segment manager. The MAC segment manager recognizes the disk label during discovery and creates EVMS segments to map the MacOS disk partitions.

6.2.7. BBR segment manager

The bad block replacement (BBR) segment manager enhances the reliability of a disk by remapping bad storage blocks. When BBR is added to a disk, it writes metadata on the disk that:

reserves replacement blocks
maps bad blocks to reserved blocks

Bad blocks occur when an I/O error is detected for a write operation. When this happens, I/O normally fails and the failure code is returned to the calling program code. BBR detects failed write operations and remaps the I/O to a reserved block on the disk. Afterward, BBR restarts the I/O using the reserve block.

Every block of storage has an address, called a logical block address, or LBA. When BBR is added to a disk, it provides two critical functions: remap and recovery. When an I/O operation is sent to disk, BBR inspects the LBA in the I/O command to see if the LBA has been remapped to a reserve block due to some earlier I/O error. If BBR finds a mapping between the LBA and a reserve block, it updates the I/O command with the LBA of the reserve block before sending it on to the disk. Recovery occurs when BBR detects an I/O error and remaps the bad block to a reserve block. The new LBA mapping is saved in BBR metadata so that subsequent I/O to the LBA can be remapped.

6.3. Adding a segment manager to an existing disk

When you add a segment manager to a disk, the segment manager needs to change the basic layout of the disk. This change means that some sectors are reserved for metadata and the remaining sectors are made available for creating data disk segments. Metadata sectors are written to disk to save information needed by the segment manager; previous information found on the disk is lost. Before adding a segment manager to an existing disk, you must remove any existing volume management structures, including any previous segment manager.

6.4. Adding a segment manager to a new disk

When a new disk is added to a system, the disk usually contains no data and has not been partitioned. If this is the case, the disk shows up in EVMS as a compatibility volume because EVMS cannot tell if the disk is being used as a volume. To add a segment manager to the disk so that it can be subdivided into smaller disk segment objects, tell EVMS that the disk is not a compatibility volume by deleting the volume information.

If the new disk was moved from another system, chances are good that the disk already contains metadata. If the disk does contain metadata, the disk shows up in EVMS with storage objects that were produced from the existing metadata. Deleting these objects will allow you to add a different segment manager to the disk, and you lose any old data.

6.5. Example: add a segment manager

This section shows how to add a segment manager with EVMS.

EVMS initially displays the physical disks it sees as volumes. Assume that you have added a new disk to the system that EVMS sees as sde. This disk contains no data and has not been subdivided (no partitions). EVMS assumes that this disk is a compatibility volume known as /dev/evms/sde.

Example 6-1. Add the DOS Segment Manager
Add the DOS Segment Manager to disk sde.

	NOTE
	In the following example, the DOS Segment Manager creates two segments on the disk: a metadata segment known as `sde_mbr`, and a segment to represent the available space on the drive, `sde_freespace1`. This freespace segment (`sde_freespace1`) can be divided into other segments because it represents space on the drive that is not in use.

6.5.1. Using the EVMS GUI

To add the DOS Segment Manager to sde, first remove the volume, /dev/evms/sde:

Select Actions->Delete->Volume.
Select /dev/evms/sde.
Click Delete.

Alternatively, you can remove the volume through the GUI context sensitive menu:

From the Volumes tab, right click /dev/evms/sde.
Click Delete.

After the volume is removed, add the DOS Segment Manager:

Select Actions->Add->Segment Manager to Storage Object.
Select DOS Segment Manager.
Click Next.
Select sde
Click Add

6.5.2. Using Ncurses

To add the DOS Segment Manager to sde, first remove the volume /dev/evms/sde:

Select Actions->Delete->Segment Manager to Storage Object.
Select /dev/evms/sde.
Activate Delete.

Alternatively, you can remove the volume through the context sensitive menu:

From the Logical Volumes view, press Enter on /dev/evms/sde.
Activate Delete.

After the volume is removed, add the DOS Segment Manager:

Select Actions->Add->Segment Manager to Storage Object
Select DOS Segment Manager.
Activate Next.
Select sde.
Activate Add.

6.5.3. Using the CLI

To add the DOS Segment Manager to sde, first tell EVMS that this disk is not a volume and is available for use:

Delete:/dev/evms/sde

Next, add the DOS Segment Manager to sde by typing the following:

Add:DosSegMgr={},sde

6.6. Removing a segment manager

When a segment manager is removed from a disk, the disk can be reused by other plug-ins. The remove command causes the segment manager to remove its partition or slice table from the disk, leaving the raw disk storage object that then becomes an available EVMS storage object. As an available storage object, the disk is free to be used by any plug-in when storage objects are created or expanded. You can also add any of the segment managers to the available disk storage object to subdivide the disk into segments.

Most segment manager plug-ins check to determine if any of the segments are still in use by other plug-ins or are still part of volumes. If a segment manager determines that there are no disks from which it can safely remove itself, it will not be listed when you use the remove command. In this case, you should delete the volume or storage object that is consuming segments from the disk you want to reuse.

6.7. Example: remove a segment manager

This section shows how to remove a segment manager with EVMS.

Example 6-2. Remove the DOS Segment Manager
Remove the DOS Segment Manager from disk sda.

	NOTE
	In the following example, the DOS Segment Manager has one primary partition on disk `sda`. The segment is a compatibility volume known as `/dev/evms/sda1`.

6.7.1. Using the EVMS GUI context sensitive menu

Follow these steps to remove a segment manager with the GUI context sensitive menu:

From the Volumes tab, right click /dev/evms/sda1..
Click Delete.
Select Actions->Remove->Segment Manager from Storage Object.
Select DOS Segment Manager, sda.
Click Remove.

6.7.2. Using Ncurses

Follow these steps to remove a segment manager with the Ncurses interface:

Select Actions->Delete->Volume.
Select /dev/evms/sda1.
Activate Delete.
Select Actions->Remove->Segment Manager from Storage Object.
Activate Remove.

6.7.3. Using the CLI

Follow these steps to remove a segment manager with the CLI:

Delete:/dev/evms/sda1

Remove: sda

Chapter 7. Creating segments

This chapter discusses when to use segments and how to create them using different EVMS interfaces.

7.1. When to create a segment

A disk can be subdivided into smaller storage objects called disk segments. A segment manager plug-in provides this capability. Another reason for creating disk segments is to maintain compatibility on a dual boot system where the other operating system requires disk partitions. Before creating a disk segment, you must choose a segment manager plug-in to manage the disk and assign the segment manager to the disk. An explanation of when and how to assign segment managers can be found in Chapter 6.

7.2. Example: create a segment

This section provides a detailed explanation of how to create a segment with EVMS by providing instructions to help you complete the following task:

Example 7-1. Create a 100MB segment
Create a 100MB segment from the freespace segment sde_freespace1. This freespace segment lies on a drive controlled by the DOS Segment Manager.

7.2.1. Using the EVMS GUI

To create a segment using the GUI, follow the steps below:

Select Actions->Create->Segment to see a list of segment manager plug-ins.
Select DOS Segment Manager. Click Next.
The next dialog window lists the free space storage objects suitable for creating a new segment.
Select sde_freespace1. Click Next.
The last dialog window presents the free space object you selected as well as the available configuration options for that object.
Enter 100 MB. Required fields are denoted by the "*" in front of the field description. The DOS Segment Manager provides default values, but you might want to change some of these values.
After you have filled in information for all the required fields, the Create button becomes available.
Click Create. A window opens to display the outcome.

Alternatively, you can perform some of the steps to create a segment from the GUI context sensitive menu:

From the Segments tab, right click on sde_freespace1.
Click Create Segment...
Continue beginning with step 4 of the GUI instructions.

7.2.2. Using Ncurses

To create a segment using Ncurses, follow these steps:

Select Actions->Create->Segment to see a list of segment manager plug-ins.
Select DOS Segment Manager. Activate Next.
The next dialog window lists free space storage objects suitable for creating a new segment.
Select sde_freespace1. Activate Next.
Highlight the size field and press spacebar.
At the "::" prompt enter 100MB. Press Enter.
After all required values have been completed, the Create button becomes available.
Activate Create.

Alternatively, you can perform some of the steps to create a segment from the context sensitive menu:

From the Segments view, press Enter on sde_freespace1.
Activate Create Segment.
Continue beginning with step 4 of the Ncurses instructions.

7.2.3. Using the CLI

To create a data segment from a freespace segment, use the Create command. The arguments the Create command accepts vary depending on what is being created. The first argument to the Create command indicates what is to be created, which in the above example is a segment. The remaining arguments are the freespace segment to allocate from and a list of options to pass to the segment manager. The command to accomplish this is:

Create: Segment,sde_freespace1, size=100MB

	NOTE
	The Allocate command also works to create a segment.

The previous example accepts the default values for all options you don't specify. To see the options for this command type:

query:plugins,plugin=DosSegMgr,list options

Chapter 8. Creating a container

This chapter discusses when and how to create a container.

8.1. When to create a container

Segments and disks can be combined to form a container. Containers allow you to combine storage objects and then subdivide those combined storage objects into new storage objects. You can combine storage objects to implement the volume group concept as found in the AIX and Linux logical volume managers.

Containers are the beginning of more flexible volume management. You might want to create a container in order to account for flexibility in your future storage needs. For example, you might need to add additional disks when your applications or users need more storage.

8.2. Example: create a container

This section provides a detailed explanation of how to create a container with EVMS by providing instructions to help you complete the following task.

Example 8-1. Create "Sample Container"
Given a system with three available disk drives (sdc, sdd, hdc), use the EVMS LVM Region Manager to combine these disk drives into a container called "Sample Container" with a PE size of 16 MB.

8.2.1. Using the EVMS GUI

To create a container using the EVMS GUI, follow these steps:

Select Actions->Create->Container to see a list plug-ins that support container creation.
Select the LVM Region Manager. Click Next.
The next dialog window contains a list of storage objects that the LVM Region Manager can use to create a container.
Select sdc, sdd, and hdc from the list. Click Next.
Enter the name Sample Container for the container and 16MB in the PE size field.
Click Create. A window opens to display the outcome.

8.2.2. Using Ncurses

To create a container using the Ncurses interface, follow these steps:

Select Actions->Create->Container to see a list of plug-ins that support container creation.
Select the LVM Region Manager. Activate Next.
The next dialog window contains a list of storage objects that the LVM Region Manager can use to create the container.
Select sdc, sdd, and hdc from the list. Activate Next.
Press spacebar to select the field for the container name.
Type Sample Container at the "::" prompt. Press Enter.
Scroll down until PE Size is highlighted. Press spacebar.
Scroll down until 16MB is highlighted. Press spacebar.
Activate OK.
Activate Create.

8.2.3. Using the CLI

The Create command creates containers. The first argument in the Create command is the type of object to produce, in this case a container. The Create command then accepts the following arguments: the region manager to use along with any parameters it might need, and the segments or disks to create the container from. The command to complete the previous example is:

Create:Container,LvmRegMgr={name="Sample Container",pe_size=16MB},sdc,sdd,hdc

The previous example accepts the default values for all options you don't specify. To see the options for this command type:

query:plugins,plugin=LvmRegMgr,list options

Chapter 9. Creating regions

Regions can be created from containers, but they can also be created from other regions, segments, or disks. Most region managers that support containers create one or more freespace regions to represent the freespace within the container. This function is analogous to the way a segment manager creates a freespace segment to represent unused disk space.

9.1. When to create regions

You can create regions because you want the features provided by a certain region manager or because you want the features provided by that region manager. You can also create regions to be compatible with other volume management technologies, such as MD or LVM. For example, if you wanted to make a volume that is compatible with Linux LVM, you would create a region out of a Linux LVM container and then a compatibility volume from that region.

9.2. Example: create a region

This section tells how to create a region with EVMS by providing instructions to help you complete the following task.

Example 9-1. Create "Sample Region"
Given the container "Sample Container," which has a freespace region of 8799 MB, create a data region 1000 MB in size named "Sample Region."

9.2.1. Using the EVMS GUI

To create a region, follow these steps:

Select Actions->Create->Region

Select the LVM Region Manager. Click Next.

	NOTE
	You might see additional region managers that were not in the selection list when you were creating the storage container because not all region managers are required to support containers.

Select the freespace region from the container you created in Chapter 8. Verify that the region is named lvm/Sample Container/Freespace. Click Next.
The fields in the next window are the options for the LVM Region Manager plug-in, the options marked with an "*" are required.
Fill in the name, Sample Region.
Enter 1000MB in the size field.
Click the Create button to complete the operation. A window opens to display the outcome.

Alternatively, you can perform some of the steps for creating a region with the GUI context sensitive menu:

From the Regions tab, right click lvm/Sample Container/Freespace.
Click Create Region.
Continue beginning with step 4 of the GUI instructions.

9.2.2. Using Ncurses

To create a region, follow these steps:

Select Actions->Create->Region.
Select the LVM Region Manager. Activate Next.
Select the freespace region from the container you created earlier in Chapter 8. Verify that the region is named lvm/Sample Container/Freespace.
Scroll to the Name field, and press spacebar.
Type Sample Region at the "::" prompt. Press Enter.
Scroll to the size field, and press spacebar.
Type 1000MB at the "::" prompt. Press Enter.
Activate Create.

Alternatively, you can perform some of the steps for creating a region with the context sensitive menu:

From the Storage Regions view, press Enter on lvm/Sample Container/Freespace.
Activate the Create Region menu item.
Continue beginning with step 4 of the Ncurses instructions.

9.2.3. Using the CLI

Create regions with the Create command. Arguments to the Create command are the following: keyword Region, the name of the region manager to use, the region managers options, and the objects to consume. The form of this command is:

Create:region, LvmRegMgr={name="Sample Region", size=1000MB},
"lvm/Sample Container/Freespace"

The LVM Region Manager supports many options for creating regions. To see the available options for creating regions and containers, use the following Query:

query:plugins,plugin=LvmRegMgr,list options

Chapter 10. Creating drive links

This chapter discusses the EVMS drive linking feature, which is implemented by the drive link plug-in, and tells how to create, expand, shrink, and delete a drive link.

10.1. What is drive linking?

Drive linking linearly concatenates objects, allowing you to create larger storage objects and volumes from smaller individual pieces. For example, say you need a 1 GB volume but do not have contiguous space available of that length. Drive linking lets you link two or more objects together to form the 1 GB volume.

The types of objects that can be drive linked include disks, segments, regions, and other feature objects.

Any resizing of an existing drive link, whether to grow it or shrink it, must be coordinated with the appropriate file system operations. EVMS handles these file system operations automatically.

Because drive linking is an EVMS-specific feature that contains EVMS metadata, it is not backward compatible with other volume-management schemes.

10.2. How drive linking is implemented

The drive link plug-in consumes storage objects, called link objects, which produce a larger drive link object whose address space spans the link objects. The drive link plug-in knows how to assemble the link objects so as to create the exact same address space every time. The information required to do this is kept on each link child as persistent drive-link metadata. During discovery, the drive link plug-in inspects each known storage object for this metadata. The presence of this metadata identifies the storage object as a link object. The information contained in the metadata is sufficient to:

Identify the link object itself.
Identify the drive link storage object that the link object belongs to.
Identify all link objects belonging to the drive link storage. object
Establish the order in which to combine the child link objects.

If any link objects are missing at the conclusion of the discovery process, the drive link storage object contains gaps where the missing link objects occur. In such cases, the drive link plug-in attempts to fill in the gap with a substitute link object and construct the drive link storage object in read-only mode, which allows for recovery action. The missing object might reside on removable storage that has been removed or perhaps a lower layer plug-in failed to produce the missing object. Whatever the reason, a read-only drive link storage object, together logging errors, help you take the appropriate actions to recover the drive link.

10.3. Creating a drive link

The drive link plug-in provides a list of acceptable objects from which it can create a drive-link object. When you create an EVMS storage object and then choose the drive link plug-in, a list of acceptable objects is provided that you can choose from. The ordering of the drive link is implied by the order in which you pick objects from the provided list. After you provide a name for the new drive-link object, the identified link objects are consumed and the new drive-link object is produced. The name for the new object is the only option when creating a drive-link.

Only the last object in a drive link can be expanded, shrunk or removed. Additionally, a new object can be added to the end of an existing drive link only if the file system (if one exists) permits. Any resizing of a drive link, whether to grow it or shrink it, must be coordinated with the appropriate file system operations. EVMS handles these file system operations automatically.

10.4. Example: create a drive link

This section shows how to create a drive link with EVMS:

Example 10-1. Create a drive link
Create a new drive link consisting of sde4 and hdc2, and call it "dl."

10.4.1. Using the EVMS GUI

To create the drive link using the GUI, follow these steps:

Select Actions->Create->Feature Object to see a list of EVMS features.
Select Drive Linking Feature.
Click Next.
Click the objects you want to compose the drive link: sde4 and hdc2.
Click Next.
Type dl in the "name" field
Click Create.
The last dialog window presents the free space object you selected as well as the available configuration options for that object.

Alternatively, you can perform some of the steps to create a drive link with the GUI context sensitive menu:

From the Available Objects tab, right click sde4.
Click Create Feature Object...
Continue creating the drive link beginning with step 2 of the GUI instructions. In step 4, sde4 is selected for you. You can also select hdc2.

10.4.2. Using Ncurses

To create the drive link, follow these steps:

Select Actions->Create->Feature Object to see a list of EVMS features.
Select Drive Linking Feature.
Activate Next.
Use spacebar to select the objects you want to compose the drive link from: sde4 and hdc2.
Activate Next.
Press spacebar to edit the Name field.
Type dl at the "::" prompt. Press Enter.
Activate Create.

Alternatively, you can perform some of the steps to create a drive link with the context sensitive menu:

From the Available Objects view, press Enter on sde4.
Activate the Create Feature Object menu item.
Continue creating the drive link beginning with step 4 of the Ncurses instructions. sde4 will be pre-selected. You can also select hdc2.

10.4.3. Using the CLI

Use the create command to create a drive link through the CLI. You