Figure 3 update copy operation, Split pair operation, Copy pace – HP XP Business Copy Software User Manual

Page 22: 3 update copy operation

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22

ShadowImage for the XP1024/XP128/XP12000/XP10000/SVS 200

NOTE:

Update copy operations do not occur every time a host issues a write I/O operation to the S-VOL

of a zSeries and SI390 pair. Update copy operations are performed asynchronously according to the

differential bitmap, which is stored in shared memory. If shared memory is lost (for example, offline micro

exchange or volatile PS on), the differential bitmap is also lost. In this case, the

XP1024/XP128/XP12000/XP10000/SVS 200 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 XP1024/XP128/XP12000/XP10000/SVS

200 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, allow extra time for SI390 operations.

Figure 3

Update Copy operation

Split Pair Operation

The SI390 split capability provides point-in-time backup of your data and also facilitates real data testing

by making the SI390 copies (T-VOLs) available for host access. The SI390 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. When the split operation is complete, the pair status changes

to split. Note 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.
While the pair is split, the disk array establishes a differential bitmap for the split S-VOL and T-VOL, and

records all updates to both volumes. When a split pair is resynced, the disk array copies all flagged tracks

from the S-VOL to the T-VOL. This method ensures that the S-VOL and T-VOL are correctly resynchronized

and also reduces the time needed to resynchronize 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. For details on

the split type, see ”

Split Type

” on page 23. Split operations cannot be performed on suspend, Resync, or

Resync-R pairs.
You can split existing SIz pairs as needed, and you can also use the split pair operation to create and split

pairs in one step. When you split an existing pair, only the differential data of the S-VOL at that time will

be copied to the T-VOL. When you create a new pair and then split that pair, whole S-VOL data will be

copied to the T-VOL. Use the Split Volume Pair window (see

Splitting ShadowImage Pairs

” on page 60) to

split existing SI390 pairs, or to add and split new SI390 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 SI390 operations on disk array I/O performance

while the faster pace splits the pairs as quickly as possible.

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