HP XP Business Copy Software - Manual (Page 13)

Figure 4 Update Copy Operation
CAUTION: If the copy operation is completed without any host I/O, the data in the P-VOL and
the data in the S-VOL may not be the same. Whether the P-VOL and the S-VOL have the same data
depends on the condition of the storage system. To make the P-VOL data and the S-VOL data equal,
split the pair and make the pair status PSUS.
•
Update copy operations are not performed for pairs with the following status: COPY(PD),
COPY(SP), PSUS(SP), PSUS, COPY(RS), COPY(RS-R), and PSUE.
•
Update copy operations do not occur every time a host issues a write I/O operation to the
P-VOL of an XP Business Copy pair. XP Business Copy update copy operations are performed
asynchronously according to the differential bitmap, which is stored in shared memory.
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If shared memory is lost (for example, during an offline micro exchange), the differential bitmap
is also lost. In this case, the storage system treats the entire volume as differential data. For
pairs with COPY(SP) or PSUS(SP) status, the storage system changes the status to PSUE due
to the loss of the differential bitmap. Note that if shared memory has been lost, extra time is
required for XP Business Copy operations, since the storage system needs to copy the entire
volume.
Split Pair Operation
The XP Business Copy split capability provides point-in-time backup of your data and also facilitates
real data testing by making the XP Business Copy copies (S-VOLs) available for host access.
The XP Business Copy pairsplit operation copies whole P-VOL data or differential data at that time
to the S-VOL to make the S-VOL identical to the P-VOL. If there are many host I/Os for the P-VOL,
it may take time to synchronize the P-VOL and the S-VOL. When the pairsplit operation is complete,
the pair status changes to PSUS. The pairsplit operations cannot be performed on the pair whose
status is PSUE, COPY(RS), or COPY(RS-R).
While the pair is split, the storage system establishes a differential bitmap for the split P-VOL and
S-VOL and records all updates to both volumes. The P-VOL remains fully accessible during the
pairsplit operation. Whether you can access the S-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, that allows you to split all the pairs in the consistency group. You can perform
XP Business Copy Operations 13