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HP XP P9500 User Manual: Handling Duplicate Volsers

Continuous access synchronous for mainframe systems.
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The CCHH (logical cylinder address and logical head address) of R0 must be identical
to the physical cylinder address and physical head address of the track.
The CCHH of each user record in a track must be unique.
Continuous Access Synchronous Z operates on volumes rather than on datasets; multivolume
datasets files require special attention. For complete duplication and recovery of a multivolume
datasets (for example, a large database file that spans several volumes), make sure that all
volumes of the file are copied to Continuous Access Synchronous Z R-VOLs.
Continuous Access Synchronous Z pair volumes can be shared with non-Continuous Access
Synchronous Z program products. See
(page 39)
Continuous Access Synchronous 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 Continuous
Access Synchronous Z pair, the R-VOL must have the same capacity as the M-VOL. Remote
Web Console displays the LVI of M-VOLs and R-VOL.
When creating multiple pairs concurrently, make sure that you set up R-VOL LDEV IDs in a
way that allows the system to correctly match them to your selected M-VOLs.
Even though you select multiple volumes as M-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 R-VOL. The system automatically assigns
LDEVs on the remote system as R-VOLs for the other selected M-VOLs according to LDEV ID.
For example, three LDEVs have been set up on the remote system to become an R-VOL, named
LDEV 01, LDEV 02, and LDEV 03. During the Add Pair operation, you select three volumes
as M-VOLs, and then select LDEV 01 as the R-VOL. The system will then assign LDEV 02 and
LDEV 03 as the R-VOL for the other two M-VOLs. Therefore, make sure that you assign LDEV
IDs to your R-VOL that will be selected in the proper order.

Handling duplicate VOLSERs

When the M-VOL is copied to the R-VOL during the initial copy operation, the M-VOL VOLSER
(Volume Serial Number) is also copied to the R-VOL. Therefore, the M-VOL and R-VOL have the
same VOLSER. Because z/OS does not allow duplicate VOLSERs, the host system administrator
must take precautions to prevent system problems related to duplicate VOLSERs (such as defining
R-VOLs not to come online automatically to the same z/OS sysplex).
If the volumes that become R-VOLs are physically attached to the same system images as the
M-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; Continuous Access Synchronous 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 R-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:
Identify the volumes that are not accessed by the host system.
Perform CHP OFF or some other operation to ensure that the volumes are inaccessible.
When performing IPL, make sure to perform LOAD CLEAR.
To avoid these problems
HP strongly recommends that your 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 R-VOL is online with hosts, all paths must be offline
from all hosts. If you cannot identify the hosts that are online, contact HP Technical Support.
Planning for Continuous Access Synchronous Z
for more information.
"Sharing Continuous Access Synchronous Z volumes"


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