HP 418800-B21 - StorageWorks Modular Smart Array 70 Storage Enclosure User Manual page 112

Synchronous operation
1.
Host data written to the virtual disks in a
source DR group is stored in a write-pending
cache on the source array.
2.
The source array replicates the data in
the write-pending cache to the destination
array.
3. The destination array writes the data to the
virtual disks in the destination DR group
and acknowledges completion back to the
source array.
4.
The source array acknowledges the writes
to the host.
Write mode states
• Asynch normal. Normal conditions for replication.
• Asynch paused. Host writes can be accepted but not replicated.
• Asynch rundown normal. Normal conditions with an increased priority to replicate from the log.
• Asynch rundown paused. Host writes can be accepted but not replicated.
• Full copy normal and full copy paused. See
• Synch normal. Normal conditions for replication.
• Synch merge normal. Also called merging. Host writes in the log are being replicated.
• Synch merge paused. Also called logging. Host writes are being stored in the log because
replication is suspended or the destination in not available.
• Unknown. Unitialized or startup state.
Write mode transitions
The write mode in a DR group pair can be changed, subject to operational considerations and technical
guidelines. See
Transition from synchronous to asynchronous
• The source DR group log cannot be
available.
• On the source and destination arrays, the disk groups specified for the logs must accommodate
the log's maximum size.
• The DR group pair cannot be suspended, failsafe enabled, or performing a full copy. See
suspension,
Transition from asynchronous to synchronous
• The DR group pair cannot be suspended.
• The DR group log (with standard asynchronous) cannot be logging.
• The transition from enhanced asynchronous does not occur until the source DR group log is run
down (merged) to the destination.
• During a transition, the log is run down or merged to the destination and host I/O is automatically
throttled. See
transition, but is expected behavior.
1 12 DR Groups
remote replication guidelines - write
logging
failsafe mode and full copy.
I/O throttling. The merging may cause an apparent delay in completing the
full copy mode.
mode.
or merging and the destination DR group must be