HP XP Cache LUN Software - Manual (Page 11)

Cache LUN XP user guide for the XP12000/XP10000/SVS200 11
Cache LUN XP support requirements for CU groups
The local disk array supports a maximum of 65,280 LDEVs for mainframe hosts and a maximum of
16,384 LDEVs for open-system hosts. LDEVs for mainframe hosts are divided into four CU groups of
16,384 LDEVs each. Each CU group is numbered from 0 to 3. If you use LDEVs from mainframe hosts for
Cache LUN XP functions, you can use LDEVs belonging to CU group 0 to CU group 3. If you use LDEVs
from open-system hosts for Cache LUN XP functions, you can use LDEVs belonging to CU group 0.
Configuration Restrictions For example, in Figure 2 , the LUSE volume is composed of three LDEVs (00:01,
1,000 LBAs, 00:02, 1,002 LBAs, and 00:03, 1,020 LBAs). If you want to set
Cache LUN XP to 500 LBAs starting from LBA number 1,020, you can set
Cache LUN XP to 500 LBAs starting from LBA number 20 on the second LDEV,
because the first LDEV size is 1,000 LBAs.
Figure 2 Example of LBA value setting with LUSE volumes
• You cannot allocate Pool-VOLs and V-VOLs for Cache LUN XP. For more
information, see the
HP StorageWorks Snapshot XP user guide.
• You cannot allocate journal volumes for Cache LUN XP.
NOTE: For more information about journal volumes, see the
HP StorageWorks Continuous Access XP Journal user guide for the
XP12000/XP10000/SVS200.
• You cannot allocate remote command devices for Cache LUN XP.
NOTE: For more information about remote command devices, see the
HP StorageWorks External Storage XP user guide.
Usage Restrictions • If an LDEV is placed in cache, do not use it for BC/Continuous Access XP quick
restore operations or Auto LUN migration. These operations may swap the
internal locations of the primary and secondary volumes and cause a loss of
data integrity.
•
You cannot change a Cache LUN XP extent after it is configured. To change the
specification, you must reset (
release
) the Cache LUN XP extent, and then
re-allocate (
set
) the Cache LUN XP extent.
CVS Automatic Resets In the following cases, a Cache LUN XP cache extent is deleted ( reset or released)
automatically:
• If a fixed volume, part or all of which is assigned to Cache LUN XP, is
converted into free space by the CVS Volume to Space function.
• If a custom volume, part or all of which is assigned to Cache LUN XP, is
converted into free space using the CVS Volume to Space function.
• If an LDEV (or VDEV) containing fixed and custom volumes assigned to Cache
LUN XP is initialized by the CVS Volume Initialize function.
Table 2
Restrictions (continued)