Filesystems, Disks and Memory

Hello,
can someobody give me the jist of understanding between network-attached storage (NAS) and storage area network (SAN) technologies ?

I looked around but didnt find any links..

Jigs

I've always been kinda fuzzy on the difference between the two myself, but here is my basic understanding of it. If anybody has better information or definitions of the two I'd be happy to be corrected . . . .

SAN is where the storage runs its own separate network, always (with maybe some rare exceptions?) over fiber. There are separate switches that connect the storage devices to each other, and you have host bus adapters in the servers that connect into those switches to access the storage.

NAS is basically just adding huge fileserver type boxes to the network. It may have direct connections to the servers or may just be accessed over the regular ethernet network.

I wanted to spend some time on our systems that use SAN before I tried to tackle this one. I don't usually work on the SAN based boxes.

As a System Administartor, SAN seems to me to be amazingly similiar to SCSI or PCI. The disks appear to be local in every respect. I can and must build filesystems on them. We even have a rack of servers with no local disks. They boot from SAN. Actually, if I want, I can use the disk area without a filesystem. We do that for swap and stuff like database chunks. . If I build a HP-UX filesystem on a SAN disk, I can mount it only on another HP-UX system. And we do that only for failover, we never attempt to use a filesystem from two systems at once. SAN "disks" are like RAID "disks". There is fault tolerance behind the scenes that is largely invisible to the OS.

Our NAS uses the nfs protocol. Many clents can mount the filesystems at once, even from very different OS's. Etc... I'm sure you guys know nfs.