Why Use SANs?

• In the past - each server had its own internal disks - hard to replace them or add more.
• Disks were moved outside (up to 7 disks per SCSI controller) - requires down-time for adding disks, many small disks for many servers cost a lot.
• Disks were moved to NAS servers (that expose CIFS or NFS shares) - not enough control by the applications (e.g. what if i want raw device access?, how does it scale to many servers and lots of TB of data? also, Ethernet performance is limiting)
• Disks were moved to RAIDs that expose block-devices directly, across a fiber-channel network.

Originally written by guy keren