Using disk mirroring

Mirroring is the duplication of the contents of an entire database device. When you set up a mirror device, all writes to the original device also go to the mirror device, and Adaptive Server reads from the original device or the mirror device based on efficiency. If one disk of a mirrored pair fails during a read or write, Adaptive Server automatically switches to the other disk and continues.

Disk mirroring provides a large benefit in recovery capability:

It prevents downtime due to disk failures.
It ensures full, nonstop recovery.
It can improve read performance because either device is available as a source.

Disk mirroring also carries a cost:

It consumes additional disk storage resources.
It slows writes because they are duplicated.

Sybase highly recommends using mirror devices if you have the resources available.

Mirroring takes place for a database device, not for a database. To mirror the activities of a database that is allocated across several devices, you must mirror all of those devices.