HP StorageWorks Continuous Access XP user guide for the XP10000/XP12000 (December 2005)

32 Continuous Access XP for the XP10000/XP12000
not support operations in which one P-VOL is copied to more than one S-VOL or more than one P-VOL is
copied to one S-VOL. Because Continuous Access XP operates on logical volumes rather than files,
multivolume files require special attention. For complete duplication and recovery of a multivolume file
(such as a large database file spanning several volumes), ensure that all volumes of the file are copied to
Continuous Access XP S-VOLs, and use Continuous Access XP Asynchronous to ensure update sequence
consistency across this group of S-VOLs.
Logical unit (LU) types
Continuous Access XP supports basic LU types that can be configured on the disk array. Continuous Access
XP displays the LU type of P-VOLs and S-VOLs. A Continuous Access XP pair must consist of LUs of the same
type and capacity (for example, OPEN-3 to OPEN-3). Mainframe volumes (for example, 3390-3A/B/C,
3380-KA/B/C) cannot be assigned to Continuous Access XP pairs.
NOTE: Contact your HP account support representative for the latest information on supported devices for
your platform.
Continuous Access XP supports the LU Size Expansion (LUSE) feature of the disk array, which configures
expanded LUs using two or more contiguous LDEVs (up to 36). If two LUSE volumes are paired with
TrueCopy, a LUSE P-VOL must be paired with an S-VOL of the same size and structure. For example, if a
LUSE P-VOL is connected with volumes of 1GB, 2GB, and 3GB in this order, you must specify the LUSE
volume that has exactly the same size and connection order as the S-VOL. When LUSE volumes are
assigned to a Continuous Access XP pair, the P-VOL and S-VOL must contain the same type and number of
LDEVs (for example, OPEN-3*6 to OPEN-3*6). The number of LDEV pairs in a Continuous Access XP LUSE
pair equals the number of LDEVs in each LUSE volume. When the status of all LDEV pairs within one
Continuous Access XP LUSE pair is not the same (for example, one LDEV pair is suspended), the pair status
of the Continuous Access XP LUSE pair changes to PDUB.
Continuous Access XP supports the VSC feature of the disk array, which configures custom-size LUs that are
smaller than standard-size LUs. When custom-size LUs are assigned to a Continuous Access XP pair, the
S-VOL must have the same capacity as the P-VOL.
Consistency groups
Continuous Access XP Asynchronous consistency groups have the following requirements:
• Each Continuous Access XP Async pair must be assigned to one and only one consistency group.
• Maximum number of volume pairs in one consistency group is 4,096 (entire RCU) (4,095 when the
RAID Manager command device is defined).
• Maximum number of consistency groups established for one MCU-RCU pair is 128 (00-7F). The RCU
supports a maximum of 128 groups, which includes both Continuous Access XP Async groups and
Mainframe mirroring Asynchronous groups (for example, 64 Continuous Access XP Async + 64
mainframe).
• Consists of only Continuous Access XP Async pairs (no mainframe pairs).
• Only Continuous Access XP Asynchronous pairs belonging to the same CLPR can be allocated to one
Continuous Access XP consistency group. For more information about CLPRs, see the HP StorageWorks
XP Disk/Cache Partition User Guide.
Accessing Continuous Access XP P-VOLs and S-VOLs
To ensure maximum data integrity during normal Continuous Access XP operations, the RCU rejects all
write operations issued by a host to a Continuous Access XP S-VOL. If you need write access to a
Continuous Access XP S-VOL, split the pair using the S-VOL write option (see ”S-VOL write option” on
page 21). When you resume (resync) the split pair, the RCU sends the S-VOL cylinder bitmap to the MCU
to ensure proper resynchronization of the pair.
Cache and nonvolatile storage (NVS)
Cache and nonvolatile storage (NVS) must be operable for both the MCU and RCU of a Continuous
Access XP volume pair. If not, the Continuous Access XP paircreate operation fails. Configure the remote