HP XP Continuous Access Software - Manual (Page 24)

primary storage system does not read the XP Continuous Access Journal secondary data volume
for a recovery.
Write and Update Copy / Write Failure
When a primary storage system receives a write I/O for a primary data volume with PAIR status,
the operation is executed at the primary storage system.
The primary storage system completes the primary data volume write operations independently of
the update copy operations at the secondary data volume. The secondary storage system updates
the data in the secondary data volume according to the write sequence number of the journal data.
This will maintain the data consistency between the primary and secondary data volumes.
Remember that the host cannot write data to the XP Continuous Access Journal primary data volume
that belongs to the journal group that was registered when the system option mode 707 is set to
ON. For information about the system option mode 707 is set to ON, see
“XP Continuous Access
Synchronous (2DC Configuration)” (page 100) .
Update Copy Failure
If the update copy operation fails, the secondary storage system suspends either the affected pair
or all XP Continuous Access Journal pairs in the journal group, depending on the type of failure.
When the suspended XP Continuous Access Journal pair or journal group is resumed (pairresync),
the primary storage system and secondary storage system negotiate the resynchronization of the
pair(s). See
“Suspend Types” (page 40) for further information on XP Continuous Access Journal
suspend types.
During normal XP Continuous Access Journal operations, the secondary storage system does not
allow XP Continuous Access Journal secondary data volumes to be online (mounted). Therefore,
hosts cannot read from and write to secondary data volumes. The XP Continuous Access Journal
secondary data volume write enable option allows write access to a secondary data volume while
the pair is split (see
“Secondary Data Volume Write Option” (page 24) ). The secondary data
volume write option can only be enabled when you split the pair from the primary storage system.
Special XP Continuous Access Journal Software Write Command
To reduce the overhead associated with these remote copy activities and maximize data transfer,
the storage system utilizes a special write command that is allowed only for XP 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 XP Continuous Access Journal write command eliminates the overhead required for
performing FBA-to-CKD and CKD-to-FBA conversions.
Secondary Data Volume Write Option
For additional flexibility, XP Continuous Access Journal provides a secondary data volume write
option (S-VOL Write) that enables write I/O to the secondary data volume of a split XP Continuous
Access Journal pair.
•
This option can be selected by the user during the pairsplit-r operation and applies only to
the selected pair(s).
•
This option can be accessed only when you are connected to the primary storage system.
When you resync a split XP Continuous Access Journal pair that 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.
24 About XP Continuous Access Journal Operations