mmcrsnapshot command

Availability

Available on all IBM Storage 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.

In IBM Storage Scale Release 4.2.1 and later, snapshot commands support the specification of multiple snapshots. Users can easily create and delete multiple snapshots. Also, system performance is increased by batching operations and reducing overhead.

# mmcrsnapshot device [[Fileset]:]Snapshot[,[[Fileset]:]Snapshot...]

# mmcrsnapshot device [[Fileset]:]Snapshot[,[[Fileset]:]Snapshot...] -j Fileset

# mmcrsnapshot device Snapshot -j Fileset1,Fileset2,...

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 information about protection against media failures, see Recoverability considerations.

For more information on global snapshots, see Creating and maintaining snapshots of file systems.

For more information on fileset snapshots, see Fileset-level snapshots.

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.

Fileset

The name of the fileset that contains the fileset snapshot to be created. If Fileset is not specified, the mmcrsnapshot command creates a global snapshot named Snapshot.

Note: Ensure that multiple snapshots and multiple filesets are not used together.

Snapshot

Specifies the name given to the snapshot.

The snapshot names are separated by a comma.

The snapshot specifier describes global and fileset snapshots. For example, Fileset1:Snapshot1 specifies a fileset snapshot named Snapshot1 for fileset Fileset1. If Fileset1 is empty, Snapshot1 is a global snapshot named Snapshot1.

Each global snapshot name must be unique from any other global snapshots. If you do not want to traverse the root of the file system 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, Snapshot 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.

Note:

• Ensure that the snapshot name does not include a colon (:) and a comma (,).
• Ensure that multiple snapshots and multiple filesets are not used together.

-j FilesetName

Creates a snapshot that includes the specified fileset and all the dependent filesets that share the same inode space. FilesetName refers to an independent fileset. If -j is not specified, the mmcrsnapshot command creates a global snapshot that includes all filesets.

If -j is specified, fileset names can be considered as a list separated by commas.

Note:

• When a list of snapshots separated by a comma (,) is used with the -j option, the fileset is applicable to each snapshot that does not use the colon (:) syntax. The fileset name must not consist of a white space.
• Only one global snapshot and one snapshot can be specified in each fileset. Therefore, multiple snapshots must not be created with the -j option. IBM® recommends that at the most one global snapshot and one fileset snapshot must be included in each independent fileset. If multiple snapshots are specified with the -j option, a snapshot with the same name is created for each fileset that has been listed.

--expiration-time

Specifies the expiration time of a snapshot for which the retention period is defined. The expiration time includes both the date and time and appears in the following format yyyy-mm-dd-hh:mm[:ss]. The snapshot cannot be deleted before the retention period expires. The defined time must be at least 10 minutes later than the current time. The maximum duration for the defined time is 365 days from the current time. For example, if the current time is 2022-07-20-20:49:00, then the valid range for the expiration time is 2022-07-20-20:59:00―2023-07-20-20:49:00.

Default snapshots, for which retention period is not defined, can be deleted any time after creation. The expiry time for all default snapshots is the same as their creation time.

You can view the defined expiration time in the mmlssnapshot command output. A sample output displaying two global snapshots and two fileset snapshots with retention periods defined for one global and one fileset snapshots is shown.

Snapshots in file system gpfs2:
Directory             SnapId          Status         Created                            ExpirationTime                Fileset
gsnap1                1                Valid        Mon Jul 4 22:49:17 2022          Mon Jul 4 22:49:17 2022
gsnap2                20               Valid        Tue Jul 26 06:00:00 2022         Mon Aug 8 12:00:00 2022
fset1-snap1           21               Valid        Tue Jul 26 06:00:40 2022         Tue Jul 26 06:00:40 2022          fset1
fset1-snap2           22               Valid        Tue Jul 26 06:01:07 2022         Fri Sep 9 12:00:00 2022           fset1

Note:

• It is optional to provide the value for [:ss] in the expiration time duration.
• If multiple snapshots are created in a single command line then they share the same expiration time.
• The --expiration-time option is available only when you upgrade the file system to format version 5.1.5 or later, or when you create the file system with version 5.1.5 or later.

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 GPFS file system.

See also

Location