Notes on using snapshot xp, Switching off the power supply, Replacing the microprogram offline – HP StorageWorks XP Remote Web Console Software User Manual
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For one snapshot data
If the same P-VOL area is updated only once, copy capacity is equal to the capacity of data written
between storing and deleting snapshot data.
For example, to make a backup using Snapshot XP, you can back up S-VOL data after storing the
snapshot data, and then delete the snapshot data. In this case, only data written during the backup
must be copied to the pool, and there is only one snapshot data. Therefore, you can make a backup
with a pool with small capacity. However, since you must read a large amount of S-VOL data during
the backup, access to the P-VOL increases and, consequently, host I/O performance might be reduced.
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For multiple snapshot data
After storing each snapshot data, if the same P-VOL area is updated only once until the snapshot data
is deleted, copy capacity is equal to the capacity of data written between storing and deleting the
snapshot data. If there is more than one P-VOL, copy capacity is equal to the total capacity of data
written to each P-VOL.
NOTE:
When you store more than one snapshot data in the pool, some Snapshot XP pairs might share
snapshot data in the pool. While snapshot data is shared, you can delete pairs, but cannot delete shared
snapshot data from the pool. Shared snapshot data is not deleted from the pool until all Snapshot XP pairs
sharing the snapshot data are deleted.
Although you estimate copied data capacity and set pool capacity according to the information in this
section, if pool capacity exceeds the threshold, implement the measures described in ”
Notes on using Snapshot XP
This section describes switching off the power supply and replacing the microprogram offline while
Snapshot XP is in use.
Switching off the power supply
Before you switch off the power supply while Snapshot XP is running, stop host I/O operations. When you
switch on the power supply, Snapshot XP behaves differently depending on whether information in shared
memory remains before and after switching off the power supply.
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If information in shared memory remains before and after switching off the power supply
You can usually use the pools and Snapshot XP pairs that you used before switching off the power.
However, since the disk array checks the status of pools and pool volumes, if pool volumes are blocked
at that time, the pool is blocked and the status of Snapshot XP pairs changes to PSUE. When this
occurs, you must recover the pools after switching the power on. For more information, see ”
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If information in shared memory is lost after switching off the power supply
The XP10000/XP12000 has a battery to maintain information in shared memory. However, when a
certain time period elapses after the breaker is turned off, the battery dies and information in shared
memory is lost. If information in shared memory is lost after switching off the power supply, information
about pools and Snapshot XP pairs is erased. Therefore, you must create pools and pairs again after
switching on the power.
For more information about the amount of time before information in shared memory is lost when the
breaker is turned off, contact your HP Account Support Representative.
Replacing the microprogram offline
Replacing the microprogram is usually performed online, but in some cases, such as when the shared
memory configuration must be changed, replacing the microprogram is performed offline. If the
microprogram is replaced offline, pool information or Snapshot XP pair information in shared memory is
lost. Therefore, you must create pools and pairs again after replacing the microprogram.