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
mmrestorefs command.
The file system must
not be remounted until the mmrestorefs command has
successfully completed.
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
system root.
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.
320 Implementing the IBM General Parallel File System (GPFS) in a Cross-Platform Environment
Silver pool, for files of large size
External pool, for near online files that are seldom accessed
Figure 8-1 Storage pools
Two types of storage pools exist:
Internal storage pools are managed within GPFS.
A system pool has the following characteristics:
Defined by default when the GPFS cluster is created
Can hold data and metadata
If no policy is defined all the data goes in system pool
When upgrading GPFS from a version without storage pools features, all the NSDs
are defined in system pool unless otherwise specified.
Metadata cannot be moved out of system storage pool, through management
policy, and it does not require placement policy to place data in.
There is only one system storage pool per file system; a file system cannot be
created without the system storage pool.
System storage pool cannot be deleted unless deleting the entire file system.
Disks inside system pool can be deleted if there is at least one disk assigned to
system pool or enough disks with space to store existing metadata.
Because system storage pool contains metadata, one should choose the premium
storage to be assigned to system pool for reason such as better performance and
failure protection.
Storage Network
GPFS
Placement
Policy
Application POSIX
GPFS
Placement
Policy
Application POSIX
GPFS
Placement
Policy
Application POSIX
GPFS
Placement
Policy
Application POSIX
System pool
User pool
Gold Pool
Silver Pool
External Pool
Tape
SATA
Disk
FC
Disk
SSD
Disk

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