Chapter 8. Information lifecycle management (ILM) 319
–The -Q flag displays whether or not quotas were automatically activated at mount time
when the snapshot was created.
– When a snapshot is restored with the mmrestorefs command, restoring the quota
activation with the mmchfs -Q command might be necessary.
Restoring a GPFS file system from a snapshot:
–Use the mmrestorefs command to restore user data and attribute files in an active file
system from the specified snapshot.
– The file system
must be unmounted from all nodes in the cluster prior to issuing the
– The file system must
not be remounted until the mmrestorefs command has
– Existing snapshots, including the one being used in the restore operation, are not
affected by the mmrestorefs command.
Linking to the GPFS snapshots
– Snapshot root directories appear in a special .snapshots directory under the file
– If you prefer to link directly to the snapshot rather than always traverse the root
directory, you may use the mmsnapdir command to add a .snapshots subdirectory to all
directories in the file system.
–The .snapshots directories that are added by the mmsnapdir command are invisible to
the ls command or to the readdir() function. This technique prevents recursive file
system utilities, such as find or tar, from entering into the snapshot tree for each
directory they process.
– Specifying the -r option on the mmsnapdir command changes back to the default
behavior, which is a single .snapshots directory in the file system root directory.
Deleting a GPFS snapshot
–Use the mmdelsnapshot command to delete GPFS snapshots of a file system.
– This command frees the space taken by the snapshot.
8.1.2 Storage pools
Physically, a storage pool is a collection of disks or RAID arrays. Storage pools also allow you
to group multiple storage systems within a file system. Using storage pools, you can create
tiers of storage by grouping storage devices based on performance, locality, or reliability
characteristics. A storage pool is an attribute for the Network Shared Disk (NSD). For
example, one pool can be an enterprise class storage system that hosts high-performance
Fibre Channel disks, and another pool might consist of numerous disk controllers that host a
large set of economical SATA disks.
Figure 8-1 on page 320 depicts an example of four nodes of a GPFS cluster that have defined
several storage pools:
System pool, for metadata information
Gold pool, for files frequently accessed
Note: The mmrestorefs command can take a long time to process, depending on
the file system size.