HP XP Business Copy Software - Manual (Page 23)

Business Copy XP user guide for the XP128/XP1024 23
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 reverse
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.
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 the entire
P-VOL track 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,
changes the status of the P-VOL and S-VOL to SMPL, accepts all subsequent write I/Os to the S-VOL,
and does not keep track of updates.
• When the disk array detects an error condition related to an update copy operation.
• When the P-VOL and/or S-VOL track map in shared memory is lost (for example, due to offline
microprogram 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.
Use the Pairsplit-E window (see ” Suspending BC pairs (Pairsplit-E) ” on page 54) to suspend BC pairs.
When a pair is suspended, the status changes to PSUE. When the pairresync operation starts, the pair
status changes to COPY(RS). The P-VOL remains fully accessible while suspended and during the
pairresync operation.
Pairsplit-S operation (delete)
This operation stops BC copy operations to the S-VOL of the pair and changes the pair status of both
volumes to SMPL. The volumes are not deleted. A BC pair can be deleted at any time except during the
quick pairsplit operation (or any status except SMPL status and PSUS(SP) status). After you delete a BC
pair, the S-VOL is still not available for write operations until the reserve attribute is reset.