HP StorageWorks XP Remote Web Console Software - Manual (Page 27)

NOTE:
When adding pairs, you can select the pace for the initial copy operations: slower, medium, or faster.
The slower pace minimizes the impact of Siz operations on storage system I/O performance, while the
faster pace completes the initial copy operations as quickly as possible.
Update Copy Operation
The Siz update copy operation updates the T-VOL of a Siz pair after the initial copy operation 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 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 6 on page 27 illustrates an update copy operation in a Siz pair with only one T-VOL.
: Duplex status
Legend
: Time flow
T-VOL S-VOL Duplex
T-VOL S-VOL
Update Copy
I/O operation
Differential Data
Host
Figure 6 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 .
Hitachi ShadowImage for z/OS user guide 27