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The usage level among parity groups is automatically rebalanced when expanding or shrinking pool
capacity operations are in progress.
If you expand the pool capacity, Thin Provisioning moves data to the added space on a per-page basis.
When the data is moved, the usage rate among parity groups of the pool-VOLs is rebalanced.
Host I/O performance may decrease when data is moved. If you do not want to have the usage level of
parity groups automatically balanced, call HPE technical support.
You can see the rebalancing progress of the usage level among parity groups in the View Pool
Management Status window in RWC. In RAID Manager, you can use the
raidcom get pool -key
command to see if the usage levels among parity groups are rebalanced. Thin Provisioning automatically
stops balancing the usage levels among parity groups if the cache memory is not redundant or the pool
usage rate reaches up to the threshold.
More information
Viewing formatted pool capacity and pool usage rates on page 154
How Fast Snap uses V-VOLs
Fast Snap uses Fast Snap V-VOLs (V-VOLs of provisioning type Snapshot in RWC, or V-VOLs created by
the
raidcom add ldev -pool snap
command in RAID Manager) or THP V-VOL as V-VOLs. Fast
Snap V-VOLs and THP V-VOLs are referred to as virtual volumes (V-VOLs) in this document. Use THP V-
VOLs to create cascaded or cloned pairs. Use Fast Snap V-VOLs to create snapshot pairs. Note that you
can use THP V-VOLs to cascade snapshot pairs.
Fast Snap uses V-VOLs to access snapshot data from hosts or clone pairs, so if you create clone pairs or
use snapshot pairs (a pair with the snapshot attribute) to access snapshot data from hosts, then V-VOLs
are required to create Fast Snap pairs or assign an S-VOL to snapshot data. If the storage system or
snapshot pair does not need to access snapshot data from hosts, V-VOLs are not necessary.
You can release the V-VOLs that are being used as Fast Snap S-VOLs from assignment of snapshot
data. Released V-VOLs can be assigned to other snapshot data. However, you cannot release allocation
of V-VOLs used as node volumes to snapshot data or allocate the V-VOL to different snapshot data. Also,
you cannot release allocation of V-VOLs which are being used for the S-VOL of a clone pair to snapshot
data, or allocate it to different snapshot data.
If you release a V-VOL being used as a Fast Snap S-VOL from assignment to snapshot data, and then
assign the V-VOL to different snapshot data, this V-VOL becomes the S-VOL of another pair. Therefore,
each time you assign a V-VOL to snapshot data, execute the command which allows the host server to
recognize the device.
You cannot release definitions of V-VOLs if the V-VOLs are being used as Fast Snap secondary volumes;
you must first release the Fast Snap pairs that are using the V-VOLs.
How Fast Snap pairs are created
Create Fast Snap pairs in the Create FS Pairs window in RWC, or by using the
raidcom add
snapshot
command in RAID Manager.
When creating a Fast Snap pair, you need to specify the pool to be used for the pair. If multiple Fast Snap
pairs share the same primary volume, the pairs must also share the same pool. For example, if you
specify three secondary volumes for one primary volume, you must specify the same pool for the three
Fast Snap pairs.
If you release a Fast Snap pair, the volume status becomes SMPL. Immediately after a volume becomes
SMPL, you cannot use the volume to create a Fast Snap pair. If you want to create Fast Snap pairs using
SMPL volumes, you should wait for a while before creating the pairs. The wait time required depends on
your system environment.
22 How Fast Snap uses V-VOLs