mmcrsnapshot command

Availability

Available on all IBM Spectrum Scale™ editions.

Description

Use the mmcrsnapshot command to create global snapshots or fileset snapshots at a single point in time. System data and existing snapshots are not copied. The snapshot function allows a backup or mirror program to run concurrently with user updates and still obtain a consistent copy of the file system as of the time the copy was created. Snapshots also provide an online backup capability that allows easy recovery from common problems such as accidental deletion of a file, and comparison with older versions of a file.

A global snapshot is an exact copy of changed data in the active files and directories of a file system. Snapshots of a file system are read-only and they appear in a .snapshots directory located in the file system root directory. The files and attributes of the file system can be changed only in the active copy.

A fileset snapshot is an exact copy of changed data in the active files and directories of an independent fileset plus all dependent filesets. Fileset snapshots are read-only and they appear in a .snapshots directory located in the root directory of the fileset. The files and attributes of the fileset can be changed only in the active copy.

Snapshots may be deleted only by issuing the mmdelsnapshot command. The .snapshots directory cannot be deleted, though it can be renamed with the mmsnapdir command using the -s option.

Because global snapshots are not full, independent copies of the entire file system, they should not be used as protection against media failures. For protection against media failures, see the IBM Spectrum Scale: Concepts, Planning, and Installation Guide and search on "recoverability considerations".

For more information on global snapshots, see "Creating and maintaining snapshots of GPFS™ file systems" in the IBM Spectrum Scale: Advanced Administration Guide.

For more information on fileset snapshots, see "Fileset-level snapshots" in the IBM Spectrum Scale: Advanced Administration Guide.

Parameters

Device

The device name of the file system for which the snapshot is to be created. File system names need not be fully-qualified. fs0 is just as acceptable as /dev/fs0.

This must be the first parameter.

SnapshotName

Specifies the name given to the snapshot.

For a global snapshot, SnapshotName appears as a subdirectory of the .snapshots directory in the root directory of the file system. Each global snapshot name must be unique from any other global snapshots. If you do not want to traverse the file system's root to access the global snapshot, a more convenient mechanism that enables a connection in each directory of the active file system can be enabled with the -a option of the mmsnapdir command.

Note: Ensure that the snapshot name is using the "@GMT-yyyy.MM.dd-HH.mm.ss" format in order to be identifiable by the Windows VSS.

For a fileset snapshot, SnapshotName appears as a subdirectory of the .snapshots directory in the root directory of the fileset. Fileset snapshot names can be duplicated across different filesets. A fileset snapshot can also have the same name as a global snapshot. The mmsnapdir command provides an option to make global snapshots also available through the .snapshots in the root directory of all independent filesets.

-j Fileset

Creates a snapshot that only includes the specified fileset plus all dependent filesets that share the same inode space. Fileset must refer to an independent fileset. If -j is not specified, the mmcrsnapshot command creates a global snapshot that includes all filesets.

Exit status

0

Successful completion.

nonzero

A failure has occurred.

Security

You must have root authority to run the mmcrsnapshot command when creating global snapshots.

Independent fileset owners can run the mmcrsnapshot command to create snapshots of the filesets they own.

The node on which the command is issued must be able to execute remote shell commands on any other node in the cluster without the use of a password and without producing any extraneous messages. For more information, see Requirements for administering a file system in IBM Spectrum Scale: Administration and Programming Reference.

See also

Location