HP StorageWorks XP Remote Web Console Software - Manual (Page 28)

NOTE:
•
Update copy operations are not performed for Siz pairs with the following status: pending, SP-pend,
V-Split, split, resync, resync-R, and suspend.
• Update copy operations do not occur every time a host issues a write I/O operation to the S-VOL of
a Siz 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 PS on), the differential bitmap is
also lost. In this case the 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
re-synchronization. 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 re-synchronization of these pairs.
If shared memory has been lost, allow extra time for Siz operations.
Split Pair Operation
The Siz split capability provides point-in-time backup of your data, and 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 performs all pending T-VOL updates (those issued prior
to the split command and recorded in the S-VOL track map) to make the T-VOL identical to the state of the
S-VOL when the split command was issued. When the split operation is complete, the pair status changes
to split. and you have full read/write access to the split T-VOL (even though it is still reserved). If there are
many host I/Os for the S-VOL, it may take time to synchronize the S-VOL and the T-VOL.
While the pair is split, the XP1024/XP128/XP12000/XP10000/SVS 200 establishes a differential
bitmap for the split S-VOL and T-VOL and records all updates to both volumes. When a split pair is
resynched, the XP1024/XP128/XP12000/XP10000/SVS 200 copies all flagged tracks from the S-VOL to
the T-VOL. This method ensures that the S-VOL and T-VOL are correctly re-synchronized and also reduces
the time needed to re-synchronize the pair. The S-VOL remains fully accessible during the split operation.
Whether you can access the T-VOL depends on what split type is specified. You cannot perform split
operations on Suspend, Resync, or Resync -R pairs.
You can split existing Siz pairs as needed, or create and split pairs in one step. When you split an
existing pair, only the differential data of the S-VOL at that time are copied to the T-VOL. When you
create a new pair and then split that pair, whole S-VOL data is copied to the T-VOL. The Split Volume Pair
dialog box allows you to split existing Siz pairs, and to add and split new Siz pairs in one step.
Copy Pace
When splitting pairs, you can select the pace for the pending update copy operation(s): slower,
medium, and faster. The slower pace minimizes the impact of Siz operations on storage system I/O
performance, while the faster pace splits the pairs as quickly as possible.
Split Type
When splitting pairs, you can also select the split type: Quick Split or Steady Split.
• When you specify 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 T-VOL is available immediately for
read and write I/Os. The whole S-VOL data or differential data at that time is copied to the T-VOL
in the background. When the quick split operation is complete, the pair status changes to split,
and you have full read/write access to the split T-VOL (even though it is still reserved). The
S-VOL also remains fully accessible.
For information about Read/Write operations from host servers to S-VOLs and T-VOLs of Siz
pairs during quick split operation.
• When you specify Steady Split:
28 Overview of Hitachi ShadowImage for z/OS Operations