Hitachi ShadowImage for z/OS user guide (HIT9503-96009, January 2008)

Add Pair Operation
The Siz add pair operation establishes the new specifiedSizpair(s).ThevolumewhichwillbetheS-VOL
must be in the simplex state, and the volume which will be the T-VOL must be reserved (if assigned
automatically) and simplex before being added to a Siz pair. The Add Pair Dialog box (see section
“Resetting the
Reserve Attribute” on page 73) allows you to add (start) new Siz volume pairs.
The CESTPAIR and PPRCOPY ESTPAIR commands allow you to add (start) Siz pairs.
SeeChapter 5 on page 99 for further information on PPRC commands.
Initial Copy Operation
Initial copy is a process where Siz copies data in an S-VOL to a T-VOL when you create a volume pair.
The Siz initial copy operation takes place when you add a new Siz pair. The initial copy operation
copies all data on the S-VOL to the associated T-VOL(s). The S-VOL remains available to all hosts for read
and write I/Os throughout the initial copy operation. Figure 5 on page 26 shows the change of the
status of a pair from the start to the end of the initial copy operation.
T-VOL S-VOL
Duplex
T-VOL S-VOL
Pending
Simplex
T-VOL S-VOL
Host
Initial Copy
I/O operation
: Duplex status
: Pending status
Legend
: Simplex status
: Time flow
Figure 5 Adding a Pair
Before the initial copy operation, the status of a pair is Simplex. The status of the pair is Pending while
the ini
tial copy operation is in progress. The status changes to Duplex when the initial copy is complete.
Write o
perations performed on the S-VOL during the initial copy operation are duplicated at the T-VOL by
updat
e copy operations after the initial copy is complete.
CAUTION:
EvenifthecopyoperationiscompletedwithoutanyhostI/O,thedataintheS-VOLandthedatain
theT-VOLmaynotbethesame.WhethertheS-VOLandtheT-VOLhavethesamedatadependson
the co
ndition 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 .
26
Overview of Hitachi ShadowImage for z/OS Operations