HP XP Business Copy Software - Manual (Page 23)

Business Copy XP user guide for the XP10000/XP12000 23
• If shared memory is lost (for example, offline micro exchange or volatile PS on), the differential bitmap
is also lost. In this case, the disk array treats the entire BC P-VOL (S-VOL for COPY(RS) pairs) as
difference data and recopies all data to the S-VOL (P-VOL for COPY(RS) pairs) to ensure proper pair
resynchronization. For pairs with COPY(SP) or PSUS(SP) status, the disk array changes the status to
PSUE due to the loss of the differential bitmap, also ensuring proper resynchronization of these pairs. If
shared memory is lost, allow extra time for BC operations.
Figure 3 Update copy operation
Cascade function
This function creates a second layer of BC volume pairs (L2) underneath the first layer of BC pairs (L1).
Cascade pairs are created by clicking Cascade instead of Set in the Paircreate window (see ” Creating BC
pairs (Paircreate) ” on page 58). This cascade layering scheme creates up to nine copies of one BC P-VOL.
See ” Cascade function ” on page 31 for further information on cascade pairs and the cascade function.
Pairsplit operation
The BC split capability provides point-in-time backup of data, and facilitates real data testing by making
the BC copies (S-VOLs) available for host access. The BC pairsplit operation copies all P-VOL data or
differential data to the S-VOL to make the S-VOL identical to the P-VOL. If there are a lot of host I/Os for the
P-VOL, it might take longer to synchronize the P-VOL and S-VOL.
Use the Pairsplit window (see ”
Splitting BC pairs (Pairsplit) ” on page 62) to split existing BC pairs or to
add and split new BC pairs in one step. When you split an existing pair, only the differential data is
copied to the S-VOL. When you create and split a new pair, all P-VOL data is copied to the S-VOL. When
the split operation is complete, the pair status changes to PSUS, and you have full read/write access to the
split S-VOL (even though it is still reserved).
While the pair is split, the disk array establishes a track map 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, and the
accessibility of the S-VOL depends on the split type (see ” Split type ” on page 23). Pairsplit operations
cannot be performed on suspended (PSUE) pairs.
Copy pace
When splitting pairs, you can select the pace for the pending update copy operation: Slower, Medium,
and Faster. The slower pace minimizes the impact of BC operations on disk array I/O performance, while
the faster pace splits the pairs as quickly as possible.
Split type
When splitting pairs, you can select the split type: Quick Split or Steady Split.
• When you specify Quick Split, the pair status changes to PSUS(SP), and the S-VOL is available
immediately for read and write I/Os (even though it is still reserved). All P-VOL data or differential
data is copied to the S-VOL in the background.
• When you specify Steady Split, the pair status changes to COPY(SP), and all P-VOL data or
differential data is copied to the S-VOL. When the operation is complete, the pair status changes to
PSUS, and you have full read/write access to the split S-VOL (even though it is still reserved). If you