Using external lus as pool-vols, Notes on using snapshot xp, Switching off the power supply – 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 storing 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 ”
Using external LUs as pool-VOLs
By using External Storage XP, you can connect multiple arrays to the XP12000/XP10000/SVS200 array.
In that case, the original XP12000/XP10000/SVS200 array is called the local array, and the connected
storage arrays are called external arrays. A volume in an external array is called an external LU. A
volume in the local array is called an internal storage virtualizer LDEV (referred to as an internal LDEV).
If External Storage XP is installed, you can use internal LDEVs and external LUs as pool-VOLs. However,
external LUs are more likely to fail than internal LDEVs. In addition, solutions for external LU failures are
more complicated than those for internal LDEV failures. To minimize the effects of failures,
HP recommends using external LUs as follows:
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Specify external LUs of only one external array for one pool
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Do not specify both internal LDEVs and external LUs as pool-VOLs in one pool
You can specify the external LUs of several external arrays for one pool, or use both internal LDEVs and
external LUs as pool-VOLs in one pool, but in that case, remember that problems such as volume blockade
can occur more easily. For example, if a problem occurs and the external LUs being used as a pool-VOL
are blocked, the pool becomes blocked as well. For more information, see ”
page 68.
For more information about external arrays and solutions for errors related to external LUs, see the
HP StorageWorks External Storage XP user guide.
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 switching off the power supply while Snapshot XP is running, stop host I/O operations. When
switching 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