Volume pairs (p-vols and s-vols) – HP StorageWorks XP Remote Web Console Software User Manual
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MCU of each XP Continuous Access pair. The MCU communicates with the RCU via dedicated
Fibre Channel remote copy connections. The MCU controls host I/O operations to the XP
Continuous Access P-VOLs and XP Continuous Access initial copy and remote copy operations
between the P-VOLs and S-VOLs. The MCU also manages XP Continuous Access pair status
and configuration information.
•
The RCU is the CU in the remote disk array that controls the S-VOLs of the XP Continuous
Access volume pairs. The RCU assists in managing XP Continuous Access pair status and
configuration (for example, rejects write I/Os to XP Continuous Access S-VOLs). The RCU
executes remote copy operations issued by the MCU. The secondary Remote Web Console
PC must be attached to the RCUs at the remote site on a separate LAN. 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 XP Continuous Access 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 XP Continuous Access to select the desired CU image in the connected MCU and
specify the desired CU image in the RCU. XP Continuous Access 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)
XP Continuous Access performs remote copy operations for logical volume pairs created by the
user. Each XP Continuous Access pair consists of one primary volume (P-VOL) and one secondary
volume (S-VOL) which can be located in different arrays. The XP Continuous Access P-VOLs are
the primary volumes (LUs) that contain the original data, and the XP Continuous Access S-VOLs
are the secondary or mirrored volumes (LUs) that 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 XP Continuous Access operations, the P-VOL remains available to all hosts at all
times for read and write I/O operations. During normal XP Continuous Access 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 option” (page 17)
).
XP Continuous Access supports the basic logical unit (LU) types available on the array (for example,
OPEN-3, OPEN-8, OPEN-9, OPEN-E, OPEN-L, and OPEN-V). XP Continuous Access 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
“Logical unit (LU) types” (page 32)
for
further information about LU requirements and support.
XP Continuous Access supports a maximum of 8,192 XP Continuous Access pairs (entire RCU).
When XP Continuous Access pairs include size-expanded LUs, the maximum number of pairs
decreases. When the RAID Manager command device is defined, the maximum number of XP
Continuous Access pairs in the array is 8,191.
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