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SAN?

N

ncage

Golden Member
Can anyone explain to me exactly what a SAN is? I know SAN system is its own network disconnected from everything else and usually the connections to a san happen over fiber but i guess my question is whats the difference say between a san and a network share or say a external raid array? Can you access a SAN just like a local drive instead of a network share? So could you like install windows xp on the san and have the computer boot up off the san?

I thought maybe in the future i would try to build an SAN off of linux that all my computers at home could use but i researched a little on google and it appears that SAN support on linux is not really stable at this point. It seems like clustering file systems are just being developed for this purpose.

Ncage
 
San stands for "Storage Array Network"

I haven't done anything in linu with it, but I have played around with Windows clustering. You put an HBA (fibre) adapter into the machine, and it connects to the array. The array provides disk space for whatever you want/need. If the OS supports it, you can install/boot from your SAN. The advantage is in clustering and speed. The SAN is fast, reliable, and redundent. If Server1 serving "webpage1" dies, server2 comes up, and has the exact same "webpage1" files that server1 did.
 
ncage, a SAN is a client/server storage system where the fundamental abstraction is a volume (disk). Contrast this with a NAS, where the fundamental abstraction is a file (or filesystem if you prefer).

NASs are best for normal everyday programs. Protocols include NFS and SMB.

SANs are best for applications where you need more control over how things are being stored. So a big database like Oracle that has its own filesystem built into it would be a better fit for a SAN. Also, if you are running a server and want to use foo-fs because it has some performance property relevant to what you're doing. Protocols include Fibre Channel and iSCSI.

On Linux, NFS is pretty solid and a lot of people use NFS, so if anything's going to work that's it. I think Fibre Channel support is also pretty solid because a FC HBA pretends to be a SCSI host adapter as far as the kernel is concerned. iSCSI is still immature. Don't know about SMB.

Most of the time, you want a NAS.

Cluster filesystems are something a bit different.
 
The #1 key concept:
A SAN simply encapsulates SCSI commands and passes them over a network instead of a SCSI cable.


This "Storage area network" is indeed fiber based. There are both loop and mesh network layouts. At one end is a server that has an HBA card which functions like a SCSI controller. On the other end is a highly available large storage array with disk space carved out to appear as multiple disks. In the middle are switches providing routing and redundancy.

That's a SAN. 🙂
 
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