HP XP External Storage Software - Manual (Page 22)

You need to assign numbers to external volume groups. See “ External Storage Requirements ” on page 43
for details on a maximum number of external volume groups, or a maximum number of volumes to be
registered in one external volume group.
Configuring External Volume Attributes
When you map an external volume as an internal volume, you set the attributes of the external
volume. External volume attributes can be set using the mapping policy or the Set External
Volume Parameter dialog box of the External Storage. For details on the mapping policy, see
“ Choosing Mapping Policy ” on page 30. For details on the Set External Volume Parameter dialog box,
see “ Set External Volume Parameter Dialog Box ” on page 72.
The attributes of the external volume are as follows:
• Emulation type
Select an emulation type for the mapped external volume from the drop-down list.
The emulation type OPEN-V must be selected if, after the mapping, you are planning to use the
existing data in the external volume from the local storage system. For example, if you want to
migrate the existing data in the external volume to the local storage system volume, you have to
set the OPEN-V emulation type when the external volume is mapped.
If you select the emulation type other than OPEN-V, the volume requires a specific area provided
for management data. Once this area is provided, volume capacity after the mapping becomes
less than the actual external volume capacity for the area (volume). For details on volume
capacity, see “ Capacity Guidelines ” on page 45.
• Cache Mode (Enable or Disable)
Cache mode specifies whether the write data from the host to the external storage system is
propagated synchronously or asynchronously. All I/O to and from the local storage system (either
Enable or Disable) always uses cache. Write operations are always backed up in duplex cache.
• If
you select Enable, after receiving the data into the local storage system cache memory,
the local storage system signals the host that an I/O operation has completed and then
asynchronously destages the data to the external storage system cache where it is then
asynchronously destaged to disk.
• If you select Disable, the local storage system signals the host that an I/O operation has
completed only after the local storage system has synchronously written the data to the
external storage system cache. The external storage system cache then asynchronously
destages this data to disk.
If you perform the HP StorageWorks XP Cache Residency Manager operation on the external
volume, which the Cache Mode is set to Disable, the bind mode of Cache Residency Manager
cannot be specified. For the Cache Residency Manager operation, see the HP StorageWorks
XP24000 Cache Residency Manager User’s Guide.
• Inflow Control (Enable or Disable)
Inflow control specifies whether the writing operation to the cache memory is stopped (Enable) or
continued (Disable) when the writing operation to the external volume is impossible. By default,
inflow control is set to Disable.
• If
you select Enable, the writing operation to cache is stopped and the I/O from the host is not
accepted when the writing operation to the external volume is impossible.
• If you select Disable, the I/O from the host during the retry operation is written to the cache
memory even after the writing operation to the external volume is impossible. Once the
writing operation to the external volume becomes normal, all the data in the cache memory
is written to the external volume (all the data is destaged).
• CLPR
When the cache memory is partitioned using HP StorageWorks XP Disk/Cache Partition,
configure a cache logical partition (CLPR) to access the mapped volume. Please see the HP
StorageWorks XP24000 Disk/Cache Partition User’s Guide for the detailed information on CLPR.
22 About External Storage Operations