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

16 Continuous Access XP for the XP10000/XP12000
reported if a problem with a secondary volume or remote disk array occurs and provide disaster
recovery capabilities.
You can define the MCU and RCU whether or not you specify the CU image. To define the MCU and RCU
and specify the CU image, specify the desired CU image. To define the MCU and RCU without specifying
the CU image, specify CU Free. For more information, see ”Registering RCUs (Add RCU)” on page 64.
The MCU and RCU can be defined separately for each Continuous Access XP volume pair. The
XP10000/XP12000 CU can function simultaneously as an MCU for one or more P-VOLs and as an RCU
for one or more S-VOLs, provided the remote copy connections and Fibre Channel or serial interface ports
are properly configured. The XP10000/XP12000 provides up to 32 logical CU images (0-1F), with each
CU image controlling up to 256 logical devices (LDEVs). To define the MCU and RCU and specify the CU
image, use Continuous Access XP to select the desired CU image in the connected MCU and specify the
desired CU image in the RCU. Continuous Access XP operations can be performed on all LDEVs except the
XP10000/XP12000 command device.
NOTE: When serial interface connections are used for remote copy operations, controller emulation of
the connected ports of the MCU and RCU can be different. However, when the MCU and RCU are
connected to the same host, controller emulation of the host-connected ports of the MCU and RCU must be
the same.
Volume pairs (P-VOLs and S-VOLs)
Continuous Access XP performs remote copy operations for logical volume pairs you create. Each
Continuous Access XP pair consists of one primary volume (P-VOL) and one secondary volume (S-VOL),
which can be in the same disk array (synchronous only) or different disk arrays. The Continuous Access XP
P-VOLs are primary volumes (LUs) containing original data, and the Continuous Access XP S-VOLs are
secondary or mirrored volumes (LUs) containing replicated or duplicate data. Volumes are copied on an
Open volume basis, and logical volumes should have the same format and capacity (SCSI path definition
is required). During normal Continuous Access XP operations, the P-VOL remains available to all hosts at
all times for read and write I/O operations. During normal Continuous Access XP operations, the RCU
rejects all host-requested write I/Os for the S-VOLs. The S-VOL write enable option allows write access to
an S-VOL while the pair is split, and uses the S-VOL and P-VOL cylinder maps to resynchronize the pair (see
”S-VOL write option” on page 21).
Continuous Access XP supports basic logical unit (LU) types available on the XP10000/XP12000.
Continuous Access XP also supports LU Size Expansion (LUSE), VSC, and HP Cache LUN XP features,
ensuring that all user data can be backed up or duplicated. See ”Logical unit (LU) types” on page 32 for
further information about LU requirements and support.
Continuous Access XP supports a maximum of 8,192 Continuous Access XP pairs (entire RCU). When
Continuous Access XP pairs include size-expanded LUs, the maximum number of pairs decreases. When
the RAID Manager command device is defined, the maximum number of Continuous Access XP pairs in
the XP10000/XP12000 is 8,191.
Continuous Access XP supports the following RAID level configurations.
Continuous Access XP Asynchronous consistency groups
A Continuous Access XP Asynchronous consistency group is a user-defined set of volume pairs across
which update sequence consistency is maintained and ensured at the remote site. Each Continuous Access
Table 3 Continuous Access XP supported RAID level configurations
For P-VOL For S-VOL
RAID 1 RAID 1
RAID 5 RAID 5
RAID 1 RAID 5
RAID 5 RAID 1