Pairs (p-vols and s-vols) – HP StorageWorks XP Remote Web Console Software User Manual
Page 12
operations between the P-VOLs and S-VOLs. The MCU also manages the XP Continuous Access
pair status and configuration information.
•
The RCU is the CU in the remote storage system that controls the S-VOLs of the XP Continuous
Access pairs. The RCU assists in managing the XP Continuous Access pair status and
configuration (for example, rejects write I/Os to XP Continuous Access S-VOLs). The RCU
executes the remote copy operations issued by the MCU. The secondary Remote Web Console
computer should 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 in case of
a problem with a secondary volume or remote storage system and to provide disaster recovery
capabilities.
You can define the MCU and RCU whether or not you specify the CU. To define the MCU and
RCU when specifying the CU, specify the desired CU. To define the MCU and RCU when not
specifying the CU, specify CU Free.
The storage system 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 ports are
properly configured. The storage system provides two logical disk controllers (LDKCs). Each LDKC
provides up to 255 logical CUs (00-FE), with each CU controlling up to 256 logical devices (LDEVs).
To define the MCU and RCU when specifying the CU, the XP Continuous Access software allows
you to select the desired CU in the connected MCU and specify the desired CU in the RCU.
XP Continuous Access operations can be performed on all LDEVs except for the storage system
command device. For further information on the storage system command device, see the HP
StorageWorks RAID Manager User Guide.
This document provides instructions for performing XP Continuous Access operations with
XP24000/XP20000 disk arrays as the MCUs. If you are using non-HP XP24000/XP20000 disk
arrays as MCUs, use the HP StorageWorks XP24000/XP20000 Continuous Access Software User
Guide for the non-storage system models.
Pairs (P-VOLs and S-VOLs)
XP Continuous Access performs remote copy operations for pairs created by the user. Each XP
Continuous Access pair consists of one primary volume (P-VOL) and one secondary volume (S-VOL),
that can be located in different storage systems. 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 a 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 18)
).
XP Continuous Access supports the basic logical unit types available on the storage system (for
example, OPEN-3, OPEN-8, OPEN-9, OPEN-E, OPEN-L, and OPEN-V). See
for further information on LU requirements and support.
XP Continuous Access supports a maximum of 32,768 pairs (entire storage system). The maximum
number of pairs is determined by the number of LDEVs, not LUs. Therefore, if the XP Continuous
Access pairs include the LUSE pairs, the maximum number of pairs decreases because a LUSE
volume consists of multiple LDEVs. When the HP StorageWorks RAID Manager command device
is defined, the maximum number of pairs in the storage system is reduced to 32,767. When XP
Continuous Access Journal for Mainframe and XP External Storage Access Manager Software pairs
exist together in the same disk subsystem, the sum of the XP Continuous Access, the XP Continuous
Access Journal, and the XP External Storage Access Manager Software pairs is used to calculate
the maximum number of pairs.
12
About XP Continuous Access Operations