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

2-10 About ShadowImage™ for IBM
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z/OS
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Operations
Hitachi ShadowImage™ for IBM
®
z/OS
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User’s Guide
Resynchronize Pair Operations
To change the status of the pairs from Split to Duplex, or from Suspend to
Duplex, you must resynchronize the pairs. ShadowImage for z/OS allows you
to perform two different types of pairresync operations: forward pairresync
operation (Normal Copy and Quick Resync) and backward pairresync operation
(Reverse Copy and Quick Copy). Forward pairresync means copying S-VOL
data to the T-VOL, and backward pairresync means copying T-VOL data to the
S-VOL.
• Normal Copy (forward pairresync in normal speed)
The normal resync operation first edits the differential bitmap of S-VOL and
T-VOL, and then (see Figure 2-6) resynchronizes the T-VOL with the S-VOL
based on the information of the edited differential bitmap. The copy
direction for a normal resync operation is S-VOL to T-VOL. Pair status
changes to Duplex when the copying process of differential data is
completed.
The pair status during a normal resync operation is resync, and the S-VOL
remains accessible to all hosts for both read and write operations during a
normal resync operation. The T-VOL becomes inaccessible to all hosts
during a normal resync operation.
• Quick Resync (forward pairresync in fast speed)
The quick resync operation first edits the differential bitmap of S-VOL and
T-VOL, and change the pair status Duplex when the editing process
completes. The differential data based on the information of the edited
differential bitmap will be copied when update copy operations are
performed for duplex pairs (see Figure 2-6). The resync operation by Quick
Resync is faster than Normal Copy since Quick Resync changes pairs status
to Duplex before actually copying differential data to the T-VOL.
The pair status during a quick resync operation is resync, and the S-VOL
remains accessible to all hosts for both read and write operations. The T-
VOL becomes inaccessible to all hosts during a quick resync operation.
Figure 2-6 illustrates the example of how the data changes during the forward
pairresync operations.