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

2–10 Compaq StorageWorks Data Replication Manager HSG80 ACS Version 8.5P Operations Guide
ORDER_ALL
When ORDER_ALL is enabled, the order of all asynchronous write operations across all
members of the association set is preserved. No log unit is required.
With the ORDER_ALL switch enabled and write history logging enabled, if one member
of the association set starts write history logging, all members of the association set start
write history logging. This allows the mini-merge to re-play the writes in the same order
received from the host.
If NOORDER_ALL is enabled, the members of the association set can start and finish
write history independently. NOORDER_ALL is the default setting.
Failover
There are two types of Failover:
■ Planned Failover (due to a planned take-down of one of the systems; for example to
perform maintenance)
■ Unplanned Failover (due to some failure within the DRM system)
Planned Failover
A planned failover allows for an orderly shutdown of controllers. The host applications
are quiesced and all write operations are permitted to complete before shutting down the
controllers so that no data is lost or jeopardized. A planned failover requires a
synchronous operation mode.
NOTE: To implement a planned failover while in asynchronous operation mode, you must first
switch to synchronous operation.
Unplanned Failover
An unplanned failover does not allow for an orderly shutdown of controllers. An
unplanned failover will be initiated when:
■ the initiator site is lost, or
■ there is no host access, or
■ there is no access to both initiator controllers.