Questions ..

SAN vs NAS...

In NAS is it true that multiple users can be accessing the same volume simultaneously? 

in SAN ... only one at a time?

Re: Questions ..

No that is not true.  SAN LUNs can be accessed by multiple "users", too.

I don't want to open up a can of worms so I'll give you MY simple definition of NAS and SAN.  Keeping in mind that every vendor has their own terminology (regarding luns, volumes, containers, etc.)... typically a NAS serves CIFS (or NFS) shares/exports to users over an ethernet network.  A SAN typically uses its own "network" (fabric) and serves block-access LUNs to hosts on the fabric.  Fibre Channel is used typically, but ISCSI protocol can also be used and travels through the ethernet network instead of a fabric.  LUNs can also be accessed by multiple hosts, but the synchronization for that access (to prevent corruption of files) is dependent on the hosts accessing the LUN.

Since NetApp's FAS/Ontap can do both... I consider it a hybrid storage solution.