HP StorageWorks XP24000 Continuous Access Journal Software User and Reference Guide, v01 (T5278-96001, June 2007)

• Split (pairsplit-r) all pairs in a journal group. See
“Splitting a Mirror (Pairsplit-r: Suspending a Copy Operation)” on page 122 for a description
of the Suspend Range-Group pairsplit-r option.
• Release (pairsplit-S) all pairs in a journal group regardless of their consistency status. See
“Deleting D ata Volumes from a Mirror (Pairsplit-S: Ending a Copy Op eration)”onpage124
for a description of the D elete Range-Group pairsplit-S option.
Read and W rit
e
I/O Operations During Continuous Access Journal Operations
When a primar
y
storage system receives a read I/O for a Continuous Access Journal primary data
volume, the
primar y storage system performs the read from the primary data volume. If the read fails,
the
redunda
ncy provided by the R A ID-1 or R AID-5 technology recovers the failure. The primary storage
system doe
s
not read the Continuous Access Journal secondary data volume for a recovery.
When a primary storage system receives a write I/O for a p rimary data volume with PAIR status, the
primary storage system performs the update copy operation, as well as writing to the primary data volume.
The primary storage system completes the primary data volume write operations independently of the
update copy operations at the secondary data volume. The secondar y storage system updates the data
in the
secondary data volume according to the write sequence numb er of the journal data. This will
maintain the data consistency between the primary and secondary data volumes. If the primary data
volume w
rite operation fails, the primary storage system reports a unit check and does not create the
journal
data for this operation. If the update copy operation fails, the secondary storage system suspends
either t
he
affected pair or all Continuous Access Journal pairs in the journal group, depending on the type
of
fail
ure. When the suspended Continuous Access Journal pair or journal group i s resumed (pairresync),
the
pri
mary storage system and secondary storage system negotiate the resynchronization of the pair(s).
See “S
uspend Types” on page 37 for further information on Continuous Access Journal suspend types.
During normal Continuous Access Journal operations, the secondary storage system does not allow
Continuous Access Journal secondary data volumes to be online (mounted). Therefore, hosts cannot
read from and write to secondary data volumes. The Continuous Access Journal secondary data
volu
me
write enable option allows write access to a secondar y data volume while the pair is split (see
“Secondary D ata Volume Write O ption” on page 29). The secondary data volume write option can only
be enabled when you split the pair from the primary storage system.
Note: To reduce the overhead associated with these remote copy activities and m aximize data transfer,
the
storage system utilizes a special write command which is allowed only for Continuous Access
Journal initial and update copy operations. This command transfers the control parameters and the
FBA
-format data for consecutive updated records in a track using a single write operation. The special
Co
ntinuous Access Journal write command eliminates the overhead required for performing FBA-to-CKD
and CKD-to-FBA conversions.
Secondary D ata Volume Write Option
For additional flexibility, Continuous Access Journal provides a secondar y data volume write option
(S-Vol. Write) which enables write I/O to the secondary data volume of a split Continuous Access Journal
pair. The secondary data volume write option can be selected by the user during the pairsplit-r operation
and
applies only to the selected p air(s). The secondary da ta volume write option can be accessed only
when you are connected to the primary storage system. When you resync a split Continuous Access
Journal pair which has the secondary data volume write option enabled, the secondary storage system
sends the secondary data volume track bitmap to the primary storage system, and the primary storage
system merges the primary data volume and secondary data volume bitmaps to determine which tracks
are out-of sync. This ensures proper resynchronization of the pair.
Difference Management
The differential data (updated by write I/Os during a split or suspension) between the primary data
volume and the secondary data volume is stored in each track bitmap. When a split/suspended pair is
resumed (pairresync) , the primary storage system merges the primary data volume and secondary data
volume bitmaps, a nd the differential data is copied to the secondary data volume.
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