HP StorageWorks Snapshot XP user guide (T1713-96021, June 2006)

28 Using Snapshot XP
Use RAID Manager XP commands to operate Snapshot XP pairs. However, whether the operations
complete normally or not depends on the pair status. Table 7 shows the pair status and results of the RAID
Manager commands.
When the command executes the process and ends normally, the pair status changes according to the
process. For more information about how the pair status changes when the command ends normally, see
Figure 4 and the corresponding text.
Notes on creating pools
When creating pools, you must be careful about the pool capacity and types of volumes specified as
pool-VOLs. This section describes notes on pool capacity definitions and using external LUs as pool-VOLs.
Defining pool capacity
Pool capacity is the total capacity of pool volumes defined in the pool. If pool capacity is insufficient, the
status of Snapshot XP pairs could change to PSUE. When creating a pool, you must estimate the copy
capacity (for example, the capacity of snapshot data to be copied to the pool) and set enough pool
capacity for the estimated copy capacity. If copy capacity changes according to the time period, set
enough pool capacity for the largest copy capacity.
NOTE:
• When snapshot data is copied to a pool, a multiple of 256 KB of the pool is used. Even if the snapshot
data capacity is less than 256 KB, you need 256 KB in the pool for the data.
• If the same P-VOL area is updated more than once, snapshot data for the area is copied to the pool
only when the first update occurs. Therefore, when the same P-VOL area is updated only once, written
data capacity is equal to copied data capacity. However, when the same P-VOL area is updated
repeatedly, copy capacity is smaller than written data capacity.
• HP recommends using a volume with a capacity that is a multiple of 256 KB as a pool-VOL. If the
capacity of the volume specified as a pool-VOL is not a multiple of 256 KB, the capacity that is less
than 256 KB is rounded off. For example, if you add a volume with 100.125 MB as a pool-VOL,
125 KB is rounded off and the pool’s capacity increases by only 100 MB.
When estimating copy capacity, consider whether there is only one snapshot data or more than one
snapshot data.
Table 7 Pair status and results of RAID Manager XP commands
Pair status RAID Manager XP command
1
1. OK: Command executes the process and ends normally.
NOP: Command does not execute the process, but ends normally.
No: Command ends abnormally (that is, command is rejected).
paircreate paircreate
-split
pairsplit pairresync pairresync
-restore
pairsplit -S pairsplit -E
SMPL OK No No No No NOP No
COPY NOP No No NOP NOP No No
PAIR/PFUL NOP OK OK NOP NOP OK No
PSUS/PFUS No NOP NOP OK OK OK No
SMPL(PD) No No No No No NOP No
COPY(RS) NOP No No NOP NOP No No
COPY(RS-R) NOP No No NOP NOP No No
PSUE NO No No OK
2
2. If you issue the pairresync command for a pair whose status has changed to PSUE because of a shortage of shared
memory for the V-VOL management area, the command is rejected and ends abnormally.
No OK NOP