HP XP P9000 Continuous Access Synchronous for Mainframe Systems User Guide

• Cnt Ac-S Z also supports Virtual LVI. This allows you to configure LVIs that are smaller than
standard LVIs. When custom-size LVIs are assigned to a Cnt Ac-S Z pair, the S-VOL must have
the same capacity as the P-VOL. Remote Web Console displays the size of P-VOLs and S-VOL.
• When creating multiple pairs concurrently, make sure that you set up S-VOL LDEV IDs in a
way that allows the system to correctly match them to your selected P-VOLs.
Even though you select multiple volumes as P-VOLs in the Remote Web Console Add Pair
procedure, only one of them displays in the dialog box—the one with the lowest LDEV ID.
Because of this, you are able to specify only one S-VOL. The system automatically assigns
LDEVs on the remote system as S-VOLs for the other selected P-VOLs according to LDEV ID.
For example, three LDEVs have been set up on the remote system to become an S-VOL, named
LDEV 01, LDEV 02, and LDEV 03. During the Add Pair operation, you select three volumes
as P-VOLs, and then select LDEV 01 as the S-VOL. The system will then assign LDEV 02 and
LDEV 03 as the S-VOLs for the other two P-VOLs. Therefore, make sure that you assign LDEV
IDs to your S-VOL that will be selected in the proper order.
Precautions for duplicate VOLSERs
When the P-VOL is copied to the S-VOL during the initial copy operation, the P-VOL VOLSER
(Volume Serial Number) is also copied to the S-VOL. Therefore, the P-VOL and S-VOL have the
same VOLSER. Because the host operating system does not allow duplicate VOLSERs, the host
system administrator must take precautions to prevent system problems related to duplicate VOLSERs
(such as defining S-VOLs not to come online automatically).
If the volumes that become S-VOLs are physically attached to the same system images as the
volumes that become the P-VOLs, the following error-prone situations may occur:
• When a pair is established using the TSO CESTPAIR command, the remote system might be
online (PPRC allows this; Cnt Ac-S Z does not). This could produce a duplex secondary online
to a host image, the results of which are not predictable.
• When a pair is released, the old S-VOL is usually offline. Then, when a host system is IPL’d
(initial program loaded), the operator is offered both volumes and asked which volume should
be left offline. You can avoid duplication of the VOLSER as follows:
1. Identify the volumes that are not accessed by the host system.
2. Perform CHP OFF or some other operation to ensure that the volumes are inaccessible.
3. When performing IPL, make sure to perform LOAD CLEAR.
To avoid such situations:
• HP strongly recommends that you specify OFFLINE=YES if the remote volumes are to be
generated in the production host’s IOCP and system generation.
• If you cannot create a pair because the S-VOL is online with hosts, all paths must be offline
from all hosts. If you cannot identify the hosts that are online, contact your HP account team.
You can obtain the information about online paths from SSBLOG of the SVP.
Preparations for allowing I/O to the S-VOL
The remote system rejects I/O to the S-VOL, unless the S-VOL-read option is enabled. The S-VOL
read option allows read-only access to an S-VOL while the pair is suspended.
• The S-VOL read option (mode 20) must be enabled by a HP representative.
• When you read an S-VOL from the host, the reference date in the VTOC is updated. In this
case, you must permit update of the VTOC.
• The CSUSPEND command to the S-VOL of a suspended pair will be rejected when the S-VOL
read option is enabled, for 2105 or 2107 controller emulation.
Planning pairs and pair volumes 35