attempt to clarify it.
SAN is a dedicated high speed network that provides access to consolidated Block Level Storage. SAN is usually connected to servers and it appears as if they are dedicated locally attached hard drive. A SAN doesn’t provide file abstraction, only block level storage. That means there is no File system associated with SAN, and you get a storage volume without any file system and you have to create the file system. You have to format the storage volume which you have got in SAN before you can start using it.
SAN supports several protocols. The most commonly used are FC, FCoE and iSCSI
NAS is a file level storage system connected to a network providing data access to a heterogeneous group of clients. So let’s say you have an External HDD. You can connect it in your router ( if it has a USB) port, use the IP adress of this drive and connect your Windows or Mac based PCs. That becomes the network drive and you can access it from any where. You don’t have to worry about formatting and file system in NAS. It’s a simple plug and play solution which is quick to deploy and is the cheapest solution available.
The most common protocols used with NAS are : SMB/ CIFS and NFS.