Storage-based mirroring overview
Some storage can improve resiliency by maintaining two or more copies of the data written by the server. The Administrator uses a storage configurator application such as Storage Navigator or Hitachi Command Suite to make mirrored copies of all the system drives (SDs) in a span. During the initial configuration, the Administrator licenses the mirrored SDs, then manually sets up the mirror relationships. Alternatively, it is possible for the server to detect the mirror relationships automatically.
Once this initial configuration has been carried out, the server can respond to storage failover without manual intervention. If a primary SD fails or becomes secondary, the file systems are unmounted. As soon as the server sees a complete set of primary SDs and no unexpected primary-primary relationships, the file systems become mountable.
The NAS server can, optionally, warn if any secondary SD fails and failover becomes impossible. The Administrator has the option of allowing or forbidding partial failovers, where the server mounts file systems on a mixture of production and backup storage. The NAS server also allows other configurations, such as mounting two copies of the same file system on different clusters.