HP StorageWorks XP Remote Web Console Software - Manual (Page 40)

If XP External Storage is installed, as well as internal volumes, external volumes can be used as
pool-VOLs. However, external volumes are more likely to fail than internal volumes. In addition,
solutions for external volume failures are more complicated than those for internal volume failures.
To minimize the effects of the failures, HP recommends that you use external volumes as follows:
•
Specify the external volumes of only one external subsystem for one pool.
•
Do not specify both internal and external volumes as pool-VOLs in one pool.
You may specify the external volumes of several external subsystems for one pool, or use both
internal and external volumes as pool-VOLs in one pool, but in that case, consider that problems
such as volume blockade may more easily happen. For example, if a problem occurs and the
external volume which is being used as a pool-VOL is blocked, the pool becomes blocked as well.
For information about how to recover the blocked pool, see
(page 96) .
For details about external subsystems and the solutions for the errors related to external volumes,
see the HP XP24000/XP20000 External Storage Software User Guide.
Requirements for Maintaining XP Snapshot
This section describes the notes on switching off the power supply or replacing the microcode
offline while XP Snapshot is in use.
Notes on Replacing the Microcode Offline
Usually, replacement of microcode is performed online, but in some cases, such as when the
configuration of the shared memory needs to be changed, replacement of microcode will be
performed offline. If the microcode is replaced offline, pool information or XP Snapshot pair
information in the shared memory will be lost. Therefore, you need to create the pools and the
pairs again after the microcode is replaced.
Notes on Switching Off the Power Supply
Before you switch off the power supply while XP Snapshot is running, stop the host I/O operations.
When you switch on the power supply again, XP Snapshot behaves differently according to whether
information in the shared memory remains before and after switching off the power supply.
•
If information in the shared memory remains before and after switching off the power supply
If information in the shared memory remains before and after switching off the power supply,
usually you can use the pools and the XP Snapshot pairs that you had been using before the
switch-off. However, because the storage system checks the status of the pools and the pool
volumes, if the pool volumes are blocked at that moment, the pool will be blocked and the
status of the XP Snapshot pairs changes to PSUE. When this occurs, you need to recover the
pools after the switch-on. For details about recovering the pools, see
(page 96) .
When you store snapshot data by a consistency group, if the power supply is switched off
before the status of all the pairs in the same consistency group has changed completely, the
storing of snapshot data will not resume, and the status of some pairs may remain unchanged
when the power supply is switched again.
•
If information in the shared memory is lost after switching off the power supply
The storage system has a battery to maintain the information in the shared memory. However,
when a certain time elapses after the breaker is turned off, the battery will die and the
information in the shared memory will be lost. If information in the shared memory is lost after
switching off the power supply, the information about the pools and the XP Snapshot pairs is
erased. Therefore, you need to create the pools and the pairs again after the switch-on.
For information about the amount of time before the information in the shared memory is lost
when the breaker is turned off, ask HP technical support.
40 Preparing for XP Snapshot Operations