Volume Pairs (P-Vols And S-Vols) - HP StorageWorks XP12000 User Manual

XP, the management station must be LAN attached to the MCU of each Continuous Access
XP pair. The MCU communicates with the RCU via dedicated Fibre Channel remote copy
connections. The MCU controls host I/O operations to the Continuous Access XP P-VOLs and
Continuous Access XP initial copy and remote copy operations between the P-VOLs and S-VOLs.
The MCU also manages Continuous Access XP pair status and configuration information.
• The RCU is the CU in the remote disk array that controls the S-VOLs of the Continuous Access XP
volume pairs. The RCU assists in managing Continuous Access XP pair status and configuration
(for example, rejects write I/Os to Continuous Access XP S-VOLs). The RCU executes remote
copy operations issued by the MCU. For Command View XP, the management station must be
LAN-attached to the RCU of each Continuous Access XP pair. For XP Remote Web Console and
Command View XP, you need connectivity between the array managed in the environment and
the Web clients used to manage them. The RCUs should also be attached to a host system to
allow sense information to be 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
The MCU and RCU can be defined separately for each Continuous Access XP volume pair. The array
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 array 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 array 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 created by the user. Each
Continuous Access XP pair consists of one primary volume (P-VOL) and one secondary volume (S-VOL)
which can be located in different arrays. The Continuous Access XP P-VOLs are the primary volumes (LUs)
which contain the original data, and the Continuous Access XP S-VOLs are the secondary or mirrored
volumes (LUs) which contain the backup or duplicate data. The primary and secondary volumes must
have the same format and capacity (and 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 differential data to resynchronize the pair
(see S-VOL write
Continuous Access XP supports the basic logical unit (LU) types available on the array (e.g., OPEN-3,
OPEN-8, OPEN-9, OPEN-E, OPEN-L, and OPEN-V). Continuous Access XP also supports the LUN
Expansion (LUSE), Virtual LVI/LUN, and Cache Residency Manager features, ensuring that all user
data can be backed up or duplicated. See
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 array is 8,191.
Continuous Access XP supports the following RAID level configurations.
16
Continuous Access XP for the Array
option).
Logical unit (LU) types for further information about LU
Registering RCUs (Add RCU).