HP StorageWorks Storage Mirroring user's guide (T2558-96073, February 2008)

14 - 25
Configuring automatic reconnections
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 will automatically start
disconnecting connections. This is called auto-disconnect. The transaction logs and system memory are flushed allowing
Storage Mirroring to begin processing anew. The auto-reconnect process ensures that any connections that were
auto-disconnected are automatically reconnected. Then, if configured, Storage Mirroring 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 will auto-reconnect. If configured, Storage Mirroring 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 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 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 source, not being able to communicate with the Storage Mirroring 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.
Target service shutdown—If the target service is stopped and restarted, there could have been data in the target queue when
the service was stopped. To prevent any loss of data, the Storage Mirroring service will attempt to persist to disk important
target connection information (such as the source and target IP addresses for the connection, various target queue
information, the last acknowledged operation, data in memory moved to disk, and so on) before the service is stopped. If
Storage Mirroring is able to successfully persist this information, when the Storage Mirroring service on the target is restarted,
Storage Mirroring will pick up where it left off, without requiring an auto-disconnect, auto-reconnect, or auto-remirror. If
Storage Mirroring cannot successfully persist this information prior to the restart (for example, a server crash or power failure
where the target service cannot shutdown gracefully), the source will auto-reconnect when the target is available, and if
configured, Storage Mirroring will auto-remirror. The remirror re-establishes the target baseline to ensure data integrity, so
disabling auto-remirror is not advised.
If you are experiencing frequent auto-disconnects, you may want to increase the amount of disk space on the volume where
the Storage Mirroring queue is located or move the disk queue to a larger volume. See
Queuing Storage Mirroring data on
page 14-22 for more information.
1. Right-click the source server on the left pane of the Management Console and select Properties.
2. Select the Setup tab.
3. Verify that the check box Automatically Reconnect During Source Initialization is marked to enable the
auto-reconnect feature.
4. Click OK to save the settings.