Szerkesztő:Gydani

A lap 2006. december 13., 17:17-kori változata

EVMS használata

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. 

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.

SCREEN

EVMS GUI

EVMSN

EVMS CLI