Hitachi ShadowImage for IBM z/OS User"s Guide (T5213-96002, June 2007)

2-14 About ShadowImage™ for IBM
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z/OS
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Operations
Hitachi ShadowImage™ for IBM
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z/OS
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User’s Guide
– During reverse copy or quick restore is in progress, you cannot perform
add, split, or resync pair for any other pair that shares the same S-VOL
(delete pair and suspend pair are allowed).
Pairresync operation time depends on the pair status, split or suspend. The
relation between the pair status and the time required for pairresync
operations are as follow:
• Pairresync for split pair
When a normal/quick resync operation is performed on a split pair, the
USP V storage system copies all differential data from the S-VOL to the
T-VOL. When a reverse copy or quick restore operation is performed on a
split pair, the storage system copies all differential data from the T-VOL to
the S-VOL. This ensures that the S-VOL and T-VOL are properly
resynchronized in the desired direction, and also greatly reduces the time
needed to resynchronize the pair.
• Pairresync for suspend pair
When a normal/quick resync operation is performed on a suspended pair,
the USP V storage system copies all data on the S-VOL to the T-VOL, since
all S-VOL tracks were flagged as difference data when the pair was
suspended. Therefore, the normal resync operation for suspended pairs is
equivalent to and takes as long as the SIz initial copy operation. If you
perform the quick resync operation on the suspended pairs, the update
copy operation will be performed and all the data will be copied to the T-
VOL. In this case, the update copy operation will be much more time than
the initial copy operation.
Delete Pair Operation
The ShadowImage for z/OS delete pair operation stops the SIz update copy
operations to the T-VOL of the pair and changes the pair status of both
volumes to simplex. An SIz pair can be deleted by the user at any time except
during the quick split operation (i.e., any status except simplex and V-split).
After you delete an SIz pair, the T-VOL is still not available for write operations
until the reserve attribute is reset.
The T-VOL of a duplex pair may not be identical to its S-VOL, due to the
asynchronous SIz update copy operations. For information about how to
synchronize the volumes before deleting the pair, see section Deleting Pairs.