Compaq StorageWorks Data Replication Manager HSG80 ACS Version 8.5P Operations Guide

2–8 Compaq StorageWorks Data Replication Manager HSG80 ACS Version 8.5P Operations Guide
When NOFAIL_ALL is specified, the members of the association set react independently
to failsafe locked conditions. One member of the association set becoming failsafe locked
has no effect on the other members of the association set. NOFAIL_ALL is the default
setting.
This switch has no effect if all members of the association set have failsafe locked error
mode disabled (normal error mode) or if there is only one remote copy set in the
association.
Write History Logging
Write history logging is a term to describe using a log unit to log a history of write
commands and data from the host. Write history logging is used for mini-merge and
fast-failback.
Mini-merge
If the target becomes inaccessible, the writes that would have gone to the target are logged
to the association set’s assigned log unit. An inaccessible target in this context refers to
both links or target controllers going down. When the target becomes accessible, a full
copy is not necessary. Only those host writes while the links were down are re-issued. This
is referred to as a mini-merge. If a full copy was in progress at the time of the disconnect,
write history logging is not initiated and the full copy is restarted when the target is
accessible again.
Fast-Failback
During a planned failover, if write history logging has been enabled at the target site, then
when the failback is performed, the initiator site is synchronized through a process called
fast-failback. The writes are logged to the target site write history log. Then, during a
fast-failback, the initiator site is updated from the write history log.