HP XP Business Copy Software - Manual (Page 30)

Use the Pairresync window to resynchronize split and suspended BC pairs. When the pairresync
operation starts, the pair status changes to COPY(RS) or COPY(RS-R). When the pairresync is complete,
the pair status changes to PAIR. The disk array resumes BC update copy operations after the pair
status changes to PAIR. The P-VOL remains fully accessible during a normal pairresync operation, but
becomes inaccessible to all hosts during a reverse or quick restore pairresync operation. This ensures
that data on the P-VOL is identical to data on the S-VOL when the reverse or quick restore pairresync
operation completes.
Pair status and time required for pairresync
The pairresync operation can be performed on a split pair or suspended pair. This section describes
the relationship between the pair status and the time required for pairresync operations.
• Pairresync for split pair. When a normal/quick pairresync operation is performed on a split pair
(status = PSUS), the disk array copies all flagged tracks from the P-VOL to the S-VOL. When a re-
verse or quick restore pairresync operation is performed on a split pair, the disk array copies all
flagged tracks from the S-VOL to the P-VOL. This ensures that the P-VOL and S-VOL are properly
resynchronized in the desired direction, and greatly reduces the time needed to resynchronize the
pair.
• Pairresync for suspended pair. When a normal/quick pairresync operation is performed on a
suspended pair (status = PSUE), the disk array copies all data on the P-VOL to the S-VOL, because
all P-VOL tracks were flagged as difference data when the pair was suspended. Reverse and quick
restore pairresync operations cannot be performed on suspended pairs. The normal pairresync
operation for suspended pairs is equivalent to and takes as long as the BC initial copy operation.
If you perform the quick pairresync operation on the suspended pairs, the update copy operation
will be performed and all the data will be copied to the S-VOL. In this case, the update copy op-
eration may take much more time than the initial copy operation.
CAUTION:
When resynchronizing pairs, you can select the pace for the pairresync operation: slower, medium,
or faster. The slower pace minimizes the impact of BC operations on subsystem I/O performance.
The faster pace resynchronizes the pairs as quickly as possible, but it may affect the disk array's I/O
performance.
Pairsplit-E operation (suspend)
This operation suspends the BC copy operations to the S-VOL of the pair. You can suspend a BC pair
at any time. When a BC pair is suspended (status = PSUE), the disk array stops performing BC copy
operations to the S-VOL, continues accepting write I/O operations to the P-VOL, and marks all P-VOL
tracks as difference data. When a pairresync operation is performed on a suspended pair, the entire
P-VOL is copied to the S-VOL. While the pairresync operation for a split BC pair can be very fast, the
pairresync operation for a suspended pair takes as long as the initial copy operation. The reverse
and quick restore pairresync operations cannot be performed on suspended pairs.
The disk array automatically suspends a BC pair when it cannot keep the pair mirrored for any reason.
When the disk array suspends a pair, sense information is generated to notify the host. The disk array
automatically suspends a pair under the following conditions:
• When the volume pair has been suspended (PSUE) or deleted (SMPL) from an open system host
using the RAID Manager command line interface.
• When the disk array detects an error condition related to an initial copy operation. When a volume
pair with COPY(PD) status is suspended (PSUE), the disk array aborts the initial copy operation,
Business Copy XP (BC) for the Array 30