Network Router User Manual

Chapter 2 Configuration Considerations 15
Choosing the Resynchronization Type: Update or Full
Tip – If a synchronization initiated by the sndradm -m or
sndradm -m -r commands is interrupted, use the sndradm -m -u update
command to complete the synchronization. Use
/usr/opt/SUNWscm/sbin/scmadm -S to view the synchronization progress.
An update resynchronization applies changes that occurred at the primary data to
thesecondarysiteduringthetimereplicationwassuspended.Theprimarysitecan
also be updated from the secondary, if desired.
A full synchronization is a complete disk-to-disk copy. This operation is the most
time consuming of the synchronization operations. A full synchronization is only
done when the Sun SNDR software volume set is:
■ Initially established
■ Damaged due to a disaster
■ Data integrity is questions
If the integrity of the Sun SNDR software volume data is questioned, then the only
way to get the volume back into a synchronized set is to perform a full volume copy.
The Sun SNDR software volume set data might be in question if, for example, there
was a double disk failure on a RAID 5 set or if the Sun SNDR software is shutdown
manually and writes occurred to either the primary or secondary volumes without
scoreboarding being active. The full copy can either be performed from the primary
to the secondary or if appropriate, from the secondary to the primary.
Choosing Automatic or Manual Resynchronization
The Sun SNDR software provides a choice of automatic or manual resynchronization
after a disaster. Automatic resynchronization is discouraged if the interruption is the
warning of a larger rolling disaster. It is best to maintain the secondary site in a
dated but consistent state, rather than risk a disastrous interruption that leaves the
secondary inconsistent and difficult to recover from. The autosynchronization option
is disabled by default for this reason.
See also “Using The Sun SNDR and Sun StorEdge Instant Image Software” on
page 16. Before you start a resynchronization operation, ensure that you have an
appropriate Instant Image software point-in-time copy of the Sun SNDR software
target volume.