HP StorageWorks XP Remote Web Console Software - Manual (Page 32)

Notes on Using External Volumes as Pool-VOLs
By using External Storage, you can connect multiple storage systems to a storage system. In that case,
the original storage system is called the local subsystem, and the connected storage systems are called
external subsystems. A volume in an external subsystem is called an external volume. A volume in
the local subsystem is called an internal volume.
If 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. In order 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, mind 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 “ Procedure to Recover a Blocked Pool ” on page 75.
For details about external subsystems and the solutions for the errors related to external volumes, see the
HP StorageWorks XP24000 External Storage Software User’s Guide.
Requirements for Maintaining XP Snapshot
This section describes the notes on switching off the power supply or replacing the microcode offline
while the 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, since 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
“ Procedure to Recover a Blocked Pool ” on page 75.
• 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.
32 Preparing for XP Snapshot Operations