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

2-6 About ShadowImage™ for IBM
®
z/OS
®
Operations
Hitachi ShadowImage™ for IBM
®
z/OS
®
User’s Guide
Write operations performed on the S-VOL during the initial copy operation will
be duplicated at the T-VOL by update copy operations after the initial copy is
complete.
Since an S-VOL remains available to all hosts for read and write I/Os during
the initial copy operation, the S-VOL might be updated during the operation.
Therefore, when the status of the pair changes to Duplex after the initial copy
operation is complete, the update copy operations take place and the
differential data of the S-VOL is copied to the T-VOL. As write I/Os are
performed on a duplex S-VOL, the USP V storage system stores the differential
bitmap, and then performs update copy operations periodically based on the
amount of differential data present on the S-VOL as well as the elapsed time
between update copy operations. Figure 2-3 illustrates an update copy
operation in a SIz pair with only one T-VOL.
: Duplex status
Legend
: Time flow
T-VOLS-VOL
Duplex
T-VOLS-VOL
Update Copy
I/O operation
Differential Data
Host
Figure 2-3 Update Copy Operation
Caution: Even if the copy operation is completed without any host I/O, the
data in the S-VOL and the data in the T-VOL may not be the same. Whether
the S-VOL and the T-VOL have the same data depends on the condition of the
storage system. To make the S-VOL data and the T-VOL data equal, split the
pair and make the pair status split.
Notes:
– Update copy operations are not performed for SIz pairs with the
following status: pending, SP-pend, V-Split, split, resync, resync-R, and
suspend.