• Remote mirroring copies the data to a remote volume as it is being written to the local volume
Pros Both copies are always 100% up to date
Synchronous Mirror
Enables Rapid recovery Primary storage
Cons
Can result in application latency during writes
Consumes SAN bandwidth Can replicate corrupted data
Remote storage
Mirrored data
Mirroring creates a real-time copy of the mirrored volumes: A write command is issued by the application to a primary storage volume. An identical write command is issued simultaneously to a backup volume.
The backup volume performs the write command and issues an acknowledgement upon completion of the command.
Mirroring can enable true fault tolerance by providing an up-to-date data copy: The backup copy is kept synchronized with the original data in real-time. If the original data storage device goes offline, hosts can automatically and transparently fail over to the backup device.
However, mirroring cannot achieve 100% reliability: If the original data is corrupted, the mirrored data will also be corrupted. When data corruption occurs with a snapshot solution, the snapshot application roll back the data to an earlier state before the corruption occurred by using the snapshot logs. This would be very difficult to achieve with a mirroring solution.