HP StorageWorks XP Remote Web Console Software - Manual (Page 33)

XP Continuous Access Split Types (PSUS)
Table 10 (page 33) lists and describes the XP Continuous Access split types. An XP Continuous
Access pair can be split by the user at any time after the initial copy operation is complete. The
user must split an XP Continuous Access pair to perform media maintenance on the P-VOL or to
access the S-VOL (S-VOL write enable).
When an XP Continuous Access Synchronous pair is split by the user, the MCU ensures
synchronization by completing any pending update copy operation before changing the status to
PSUS. After the pair status changes to PSUS, the MCU stops performing update copy operations
to the S-VOL and may or may not continue accepting write I/Os for the P-VOL, depending on the
P-VOL fence level and pairsplit options. If the P-VOL accepts write operations while the pair is split,
the MCU records the data in the P-VOL tracks that are updated as differential data. If you enabled
the S-VOL write option when you split the pair, the RCU records the data in the S-VOL tracks that
are updated while the pair is split as differential data. When the pair is resynchronized (pairresync),
the RCU sends the S-VOL differential data to the MCU, and the MCU merges the P-VOL and S-VOL
differential data to determine which tracks are out-of-sync.
When XP Continuous Access Synchronous and Asynchronous pairs exist in the same storage system,
and there are host I/Os to the XP Continuous Access Asynchronous Software pairs, if you split XP
Continuous Access Asynchronous pairs of which the P-VOL Fence Level option is Data, you must
stop the host I/Os before split operation. If you do not stop host I/Os, the pairs might be forcibly
suspended because of a timeout error, and host I/Os will be rejected.
When an XP Continuous Access Asynchronous pair is split by the user, the MCU and RCU ensure
synchronization by either completing or discarding any pending update copy operations according
to the setting of the Pending Update option. The MCU and RCU keep track of any recordsets that
were discarded during the pairsplit operation. After the pair status changes to PSUS, the MCU
stops performing recordset operations for the pair, continues accepting write I/Os for the split XP
Continuous Access Asynchronous P-VOL, and records the data in the P-VOL tracks that are updated
while the pair is split as differential data. If you enabled the S-VOL write option when you split the
pair, the RCU also records the S-VOL tracks that are updated while the pair is split as differential
data. When the pair is resynchronized, the RCU sends the S-VOL differential data to the MCU,
and the MCU merges the P-VOL and S-VOL differential data to determine which tracks are
out-of-sync.
A split (or suspended) XP Continuous Access Asynchronous S-VOL has an additional status called
the consistency status. The consistency status is displayed only at the RCU and indicates the S-VOL’s
update sequence consistency with respect to the other S-VOLs in the same group.
Table 11 (page
34) lists and describes the consistency statuses for split or suspended XP Continuous Access
Asynchronous S-VOLs (the consistency status is displayed only at the RCU).
Table 10 Split Types (PSUS)
Description Applies to Type
The user split the pair from the MCU using the P-VOL Failure for the
Suspend Kind option. The S-VOL split type is PSUS-by MCU. P-VOL
(XP Continuous
Access Synchronous
only)
PSUS, P-VOL
by Operator
The user split the pair from the MCU or RCU using the S-VOL option
for the Suspend Kind option. P-VOL, S-VOL PSUS, S-VOL
by Operator
The RCU received a request from the MCU to split the pair. The P-VOL
split type is P-VOL by Operator or S-VOL by Operator. S-VOL PSUS, by
MCU
The MCU detected that the S-VOL status changed to SMPL because
the user released the pair (pairsplit-S) from the RCU. The pair cannot P-VOL PSUS, Delete
pair to RCU
be resynchronized because the S-VOL does not have the PSUS or
PSUE status.
Pair Status 33