I am from a software background so I am not really up to date with these storage technology.
I am asked this question today and I don't feel like I am able to give a correct answer.
Here is my understanding:
SAN refers to a set of low level of technology which ensures high availability of data storage.
NAS is a more generic term which refers to any device that provides access to storage over a network.
Are they correct? Did I miss any key features?
The general difference between SAN and NAS is that SAN is block level (In other words the device accessing the remote storage assigns a file system to the drive) and that NAS is file level (The device hosting the NAS provides a file system for the drive and the device accessing the remote device sees them through a protocol such as NFS or CIFS/SMB.) SANs will be faster, generally, due to the effects of transmitting block-level information instead of file-level information.
There are other things that are implied with the name "Storage Area Network" or SAN, but high availability isn't a requirement of them. Again, generally speaking if someone is talking about a SAN, they are referring to a drive or group of drives that are available at the block level through iSCSI, FC or FCoE, while someone speaking of a NAS will be speaking of a fileserver such as a linux box that is running NFS and Samba with the file system written by the hosting device.
forget all the fancy wording and specific cases like FC, FoE, iSCSI, etc.
SAN is a network (real or virtual, ethernet, fiber, or homing pigeon) exclusively for providing and using data storage. Though people also use SAN for the storage devices connected to a SAN too.
NAS is a storage device connected to a network that also does other things.
You can buy a "NAS box" and connect it to a SAN, so the NAS becomes a SAN device.
Think outside the box: If you had a station wagon used exclusively for transporting disks, tapes, etc with data on them you could call that a SAN with sneakernet connectivity.
NAS- cheap, slow shared storage over shared network
SAN- expensive, fast storage over dedicated network
