HP XP Continuous Access Software - Manual (Page 16)

16 Continuous Access XP for the XP1024/XP128
information to be reported if a problem with a secondary volume or remote disk array occurs and
provide disaster recovery capabilities.
The MCU and RCU can be defined separately for each Continuous Access XP volume pair. The
XP1024/XP128 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 XP1024/XP128 provides up to 32 logical CU images (0-1F), with each CU
image controlling up to 256 logical devices (LDEVs). Use Continuous Access XP to select the CU image in
the connected MCU and specify the CU image in the RCU. Continuous Access XP operations can be
performed on all LDEVs except the XP1024/XP128 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 20).
Continuous Access XP supports basic logical unit (LU) types available on the XP1024/XP128. Continuous
Access XP also supports LU Size Expansion (LUSE), Custom Volume Size (CVS), and Cache LUN XP
features, ensuring that all user data can be backed up or duplicated. See ” Logical unit (LU) types ” on
page 31 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 XP1024 is 8,191 (4,095 in the XP128).
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 XP Async volume pair must be assigned to a consistency group. Continuous Access XP can
configure up to 128 consistency groups (0-7F) for each MCU and provides group-based operations for
consistency groups (for example, split and resync group). Use consistency groups to maintain update
sequence consistency for databases spanning multiple volumes, allowing immediate database recovery at
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