I'm always confused when people talk about NAS, SAN or DAS. I just found this interesting comment on serverfault.com:
First it is best to define the difference between a block device and filesystem. This is easier grasped if you are familiar with UNIX because it makes an objective distinction between the two things. Still the same applies to Windows.
- A block device is a handle to the raw disk.
- Such as /dev/sda for a disk or /dev/sda1 for a partition on that disk.
- A filesystem is layered on top of the block device in order to store data. You can then mount this.
- Such as mount /dev/sda1 /mnt/somepath.
With those terms in mind it's then easier to see the distinction between the following.
- DAS is a block device from a disk which is physically [directly] attached to the host machine.
- You must place a filesystem upon it before it can be used.
- Technologies to do this include IDE, SCSI, SATA, etc.
- SAN is a block device which is delivered over the network.
- Like DAS you must still place a filesystem upon it before it can used.
- Technologies to do this include FibreChannel, iSCSI, FoE, etc.
- NAS is a filesystem delivered over the network.
- It is ready to mount and use.
- Technologies to do this include NFS, CIFS, AFS, etc.