HP XP Business Copy Software - Manual (Page 23)

NOTE:
•
Update copy operations are not performed for pairs with the following status: COPY(PD) ( pending
duplex), COPY(SP) (steady split pending), PSUS(SP) (quick split pending), PSUS (split), COPY(RS)
(
resync), COPY(RS-R) (resync-reverse), and PSUE (suspended).
• Update copy operations do not occur every time a host issues a write I/O operation to the P-VOL
of a BC pair. BC update copy operations are performed asynchronously according to the differ-
ential 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 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) ). This cascade layering scheme creates up to nine copies of one BC
P-VOL. See Cascade function for further information on cascade pairs and the cascade function.
Pairsplit operation
The BC split capability, by making the BC copies (S-VOLs) available for host access, provides a
point-in-time copy that can be used for data backup or to provide real data for test purposes. 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 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).
XP Business Copy User Guide 23