HP StorageWorks XP Remote Web Console Software - Manual (Page 20)

data. Performing pairresync on a suspended pair is similar to making an initial copy and is not as fast as
performing pairresync on a split pair.
The storage system will automatically suspend a Business Copy pair when it cannot keep the pair mirrored
for any reason. When the storage system suspends a pair, sense information is generated to notify the
host. The storage system will automatically suspend a pair under the following conditions:
• When the storage system detects an error condition related to an update copy operation.
• When the differential bitmap in shared memory is lost (for example, due to offline microcode
exchange). This applies to COPY(SP) and PSUS(SP) pairs only. For PAIR, PSUS, COPY(RS), or
COPY(RS-R) pairs, the pair is not suspended but the entire P-VOL (S-VOL for reverse or quick
restore pairresync) is marked as difference data.
Resynchronize Pair Operations
To change the status of the pairs from PSUS to PAIR, or from PSUE to PAIR, you must resynchronize
the pairs. Business Copy allows you to perform four different types of pairresync operations: forward
pairresync (Normal Copy and Quick Resync) and backward pairresync (Reverse Copy and Quick Copy).
Forward pairresync means copying P-VOL data to the S-VOL, and backward pairresync means copying
S-VOL data to the P-VOL.
• Normal Copy (forward pairresync in normal speed)
The normal pairresync operation (see Figure 6 on page 21) first reads the differential bitmap of
the P-VOL and S-VOL, and then resynchronizes the S-VOL with the P-VOL based on the differential
bitmap. The copy direction for a normal pairresync operation is P-VOL to S-VOL. Pair status
changes to PAIR when the copying process of differential data completes. The pair status during
a normal pairresync operation is COPY(RS), and the P-VOL remains accessible to all hosts for
both read and write operations during a normal pairresync.
• Quick Resync (forward pairresync in fast speed)
The quick pairresync operation (see Figure 6 on page 21) first reads the differential bitmap of
P-VOL and S-VOL, and then changes the pair status to PAIR. The differential data based on the
differential bitmap will be copied when update copy operations are performed for the pair in
PAIR status. The pairresync operation by Quick Resync is faster than Normal Copy since Quick
Resync changes pair status to PAIR before actually copying differential data to the S-VOL.
The pair status during a quick pairresync operation is COPY(RS), and the P-VOL remains
accessible to all hosts for both read and write operations. The S-VOL becomes inaccessible to
all hosts during a quick pairresync operation.
Figure 6 on page 21 illustrates how the data changes during the forward pairresync operations.
20 About Business Copy Operations