HP StorageWorks XP24000 Continuous Access Software User and Reference Guide, v01 (T5278-96002, June 2007)

Pair Status Description P-VOL
Access
S-VOL
Access
Pair Status for Con tinuous Access Asynchronous o n ly:
Suspending
This pair is not synchronized. This pair is in transition
from PA IR or COPY to PSUS/PSUE. When the
split/suspend pair operation is requested, the status
of
all affected pairs changes to Suspending.When
the split/suspend operation is complete, the status
changes to PSUS/PSUE.
Read/write
Read only
Deleting
This pair is n
ot
synchronized. This pair is in transition
from PAIR, C
OPY, or PSUS/PSUE to SMPL. Wh en
the pairspl
it-S
operation is requested, the status of
all affecte
d
pairs changes to Deleting.When the
pairsplit
-S
operation is complete, the status changes
to
SMPL.
Read/write
Read only
Continuous Access Split Types (PSUS)
Table 6 on page 30 lists a nd describes the Continuous Access split types. A Continuous Access pair
can
be split by the user at any time after the initial co py operation is complete. The user must split a
Continuous Access pair in ord er to perform media maintenance on the P-VOL or to access the S-VOL
(S-VOL write enable).
When a 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 p er forming 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 d ata.
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.
Note: You must stop host I/Os before splitting Continuous Access Synchronous pa irs with the Data
fence level and the following conditions: Continuous Access Synchronous and Asynchronous pairs exist
in the
same storage system, and there are host I/Os to the Continuous Access Asynchronous pairs. 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 rej ected.
When a Continuous Access Asynchrono us 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
user-specified drain/purge p a irsplit 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 acc epting write I /O s for the split 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-VO L differential data to the MCU, and the MCU m erges the P-VOL
and
S-VOL differential data to determine which tracks are out-of-sync.
A split (or suspended) 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 7 on page 30 lists and
describes the c onsistency statuses for split or suspended Continuous Access Asynchronous S-VOLs (the
consistency status is displayed only at the RCU).
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