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

About ShadowImage™ for IBM
®
z/OS
®
Operations 2-7
Hitachi ShadowImage™ for IBM
®
z/OS
®
User’s Guide
– Update copy operations do not occur every time a host issues a write
I/O operation to the S-VOL of a ShadowImage for z/OS® pair. SIz
update copy operations are performed asynchronously according to the
differential bitmap, which is stored in shared memory.
– If shared memory is lost (e.g., offline micro exchange, volatile power
supply on), the differential bitmap is also lost. In this case the USP V
storage system treats the entire S-VOL (T-VOL for resync-R pairs) as
difference data and recopies all data to the T-VOL (S-VOL for resync-R
pairs) to ensure proper pair resynchronization. For pairs with SP-pend
or V-Split status, the storage system changes the status to suspend due
to the loss of the differential bitmap, ensuring proper resynchronization
of these pairs. If shared memory has been lost, extra time is required
for SIz operations, since the USP V needs to copy the entire volume.
Split Pair Operation
The ShadowImage for z/OS split capability provides point-in-time backup of
your data, and also facilitates real data testing by making the SIz copies
(T-VOLs) available for host access. The SIz split operation copies whole S-VOL
data or differential data at that time to the T-VOL to make the T-VOL identical
to the state of the S-VOL when the split command was issued. If that if there
are many host I/Os for the S-VOL, it may take time to synchronize the S-VOL
and the T-VOL. When the split operation is complete, the pair status changes
to split. Note that the split operations cannot be performed on the pair whose
status is suspend, resync or resync-R.
While the pair is split, the USP V storage system establishes a differential
bitmap for the split S-VOL and T-VOL and records all updates to both
volumes. The S-VOL remains fully accessible during the split operation.
Whether you can access the T-VOL depends on what split type is specified.
There are two kinds of split types, Quick Split and Steady Split. In addition to
the split types, there is At-Time Split which allows you to split all the pairs in
the consistency group. You can perform Quick Split and Steady Split in the
Split Volume Pair dialog box. On the other hand, you need Business Continuity
Manager to perform At-Time Split.
• Split pair operation by Quick Split:
When the quick split operation starts, the pair status changes to V-split.
You have full read/write access to the split T-VOL (even though it is still
reserved). The whole S-VOL data or differential data at that time will be
copied to the T-VOL in the background.
For information about Read/Write operations from host servers to S-VOLs
and T-VOLs of SIz pairs during quick split operation, see Table 5-2.
• Split pair operation by Steady Split: