How Storage Area Network differs from RAID?

Answer 1

Those two technologies have nothing incomon except for the fact that both address mass storages. RAID is a technology to span data over multiple disks to either gain more speed (seldom e.g. RAID0) or gain redundancy so that the system remains functional when one of the mass storages fail (e.g. RAID1 or RAID5). SAN means that there is a dedicated network instead of a local bus connecting the hostadapter to the storage. These networks use often similar protocol as on a local buses (e.g. iSCSI). Data is not aqured on a file per file base like in a server instead the host requests the specific blocks he would like to read. Advantages of a SAN may be fast switch over of mass storages from one Node to an other (storage failover if a node fails), storage sharing (one big disk [might even be a RAID system] is split up into two or more "virtual" disks which are then handeled by the respective node) or a centralized fast access for backup storages. Important thing to know is: both technologies may be (and are often) combined to get the best of both worlds.