Diffrence SAN & NAS

NAS	SAN
NAS uses TCP/IP Networks: Ethernet, FDDI, ATM (perhaps TCP/IP over Fibre Channel someday)	SAN uses Fibre Channel.
NAS uses File Server Protocols: NFS, CIFS, HTTP.	SAN uses Encapsulated SCSI.
Almost any machine that can connect to the LAN (or is interconnected to the LAN through a WAN) can use NFS, CIFS or HTTP protocol to connect to a NAS and share files.	Only server class devices with SCSI Fibre Channel can connect to the SAN. The Fibre Channel of the SAN has a limit of around 10km at best
A NAS identifies data by file name and byte offsets, transfers file data or file meta-data (file's owner, permissions, creation data, etc.), and handles security, user authentication, file locking	A SAN addresses data by disk block number and transfers raw disk blocks.
A NAS allows greater sharing of information especially between disparate operating systems such as Unix and NT.	File Sharing is operating system dependent and does not exist in many operating systems.
File System managed by NAS head unit	File System managed by servers
Backups and mirrors (utilizing features like NetApp's Snapshots) are done on files, not blocks, for a savings in bandwidth and time. A Snapshot can be tiny compared to its source volume.	Backups and mirrors require a block by block copy, even if blocks are empty. A mirror machine must be equal to or greater in capacity compared to the source volume.