HP StorageWorks XP Remote Web Console Software - Manual (Page 18)

: PAIR status
S-VOL P-VOL PAIR
S-VOL P-VOL
Differential Data
I/O operation
Host
Update Copy
Legend
: Time flow
Figure 4 Update Copy Operation
Caution: Even 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.
Notes:
• 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. For details about pair status,
see Table 2 on page 26.
• Update copy operations do not occur every time a host issues a write I/O operation to the P-VOL
of a Business Copy pair. Business Copy update copy operations are performed asynchronously
according to the differential bitmap, which is stored in shared memory.
• 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
Business Copy operations, since the storage system needs to copy the entire volume.
Split Pair Operation
The Business Copy split capability provides point-in-time backup of your data, and also facilitates real
data testing by making the Business Copy copies (S-VOLs) available for host access.
The 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. Note that 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,
which allows you to split all the pairs in the consistency group. You can perform Quick Split and Steady
Split in the Pairsplit dialog box. On the other hand, you need RAID Manager to perform At-Time Split.
• Pairsplit by Quick Split
18 About Business Copy Operations