HP StorageWorks Storage Mirroring Recover User's Guide (T5437-96008, November 2009)

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Auto-disconnect and auto-reconnect
While disk queues are user configurable and can be extensive, they are limited. If the
amount of disk space specified for disk queuing is met, additional data could not be
added to the queue and data would be lost. To avoid any data loss, the auto-disconnect
and auto-reconnect processes occur.
● Exhausted queues on the source—If disk queuing is exhausted on the source,
Storage Mirroring Recover will automatically start disconnecting connections. This
is called auto-disconnect. The transaction logs and system memory are flushed
allowing Storage Mirroring Recover to begin processing anew. The auto-reconnect
process ensures that any connections that were auto-disconnected are
automatically reconnected. Then, if configured, Storage Mirroring Recover will
automatically remirror the data. This process is called auto-remirror. The remirror
re-establishes the target baseline to ensure data integrity, so disabling auto-
remirror is not advised.
● Exhausted queues on the target—If disk queuing is exhausted on the target, the
target instructs the source to pause. The source will automatically stop transmitting
data to the target and will queue the data changes. When the target recovers, it will
automatically tell the source to resume sending data. If the target does not recover
by the time the source queues are exhausted, the source will auto-disconnect as
described above. The transaction logs and system memory from the source will be
flushed then Storage Mirroring Recover will auto-reconnect. If configured, Storage
Mirroring Recover will auto-remirror. The remirror re-establishes the target baseline
to ensure data integrity, so disabling auto-remirror is not advised.
● Queuing errors—If there are errors during disk queuing on either the source or
target, for example, Storage Mirroring Recover cannot read from or write to the
transaction log file, the data integrity cannot be guaranteed. To prevent any loss of
data, the source will auto-disconnect and auto-reconnect. If configured, Storage
Mirroring Recover will auto-remirror. The remirror re-establishes the target baseline
to ensure data integrity, so disabling auto-remirror is not advised.
● Target server interruption—If a target machine experiences an interruption (such
as a cable or NIC failure), the source/target network connection is physically
broken but both the source and target maintain the connection information. The
Storage Mirroring Recover source, not being able to communicate with the Storage
Mirroring Recover target, stops transmitting data to the target and queues the data
changes, similar to the exhausted target queues described above. When the
interruption is resolved and the physical source/target connection is reestablished,
the source begins sending the queued data to the target. If the source/target
connection is not reestablished by the time the source queues are exhausted, the
source will auto-disconnect as described above.