SAN

Khannie

Can someone explain to me what the point of a SAN is if not to provide shared disk access to > 1 machine?

I thought a SAN allowed you to locally mount shared storage.

ressem

The SAN can be used by multiple machines simultaneously, but the storage space is divided into LUNs, each of which can be a section of a disk, a disk array or anything in between.

LUNs like the partitioned file systems on a local computer, can only safely be controlled by one server at a time.
By default you can't even have a second server with read-only access to the file system at the same time without taking a snapshot.

But using masking, zoning and/or pricy software a server can do things like scheduling time at which it will have control of a LUN.

It's meant to give the admin the ability to avoid overspecifying server storage and backup at purchase time, as they can instead assign another LUN as needs be.
Throwing great big loads of data between servers or backup devices is faster, and less reliant on individual machine configurations and tools.
The elements of the SAN do not have to be in the same location.

Khannie

Nice one. That makes sense. Thanks.

What I'd really like is a SAN with NAS type capability then I suppose. To be honest, it seems like the kind of functionality that holy **** expensive kit like that should have built into it.

ressem

Yep you can put a NAS on top of a SAN, but if that's all you do, the boss will wonder why a cheaper NAS box wasn't bought.
Usually you'd have a NAS cluster on top, to allow for failover, or to advertise 99.99% uptime.

What crowds like HP storageworks will do is they will configure a cluster on top of the SAN, using Sun's Lustre clustered file system for HP I think, which means the operating system makes the IO requests from lightweight servers which manage all the location information so clients are allowed controlled access to specific blocks of the file system.

Its possible that when configured well for client accesses to be quicker than a NAS using NFS or the like, especially if client applications use the lustre library to make the file system calls, or so I've read in the brochure.

You have Oracle cluster software for Oracle DBs on SAN, Redhat have GFS etc.
http://www.redhat.com/magazine/006apr05/features/gfs/

ob

QNAP do some iSCSI/NAS stuff aimed at the lower end of the market.

Khannie

Ah this is for a work install in a faraway place where money isn't a problem. Really I wanted the performance of a SAN with the sharing of a NAS and I'm still learning about high end hardware so I assumed the S in SAN meant shared as in really shared.

jim_bob

have a look at the dell equal logic boxes

Rew

Handy budget SAN is a Thecus N7700. Can take 10TB+ of disk and present it over NAS or iSCSI. You can do clustered file systems with the likes of Oracle Cluster File System (OCFS). I use that on a Fiber Channel SAN to share storage between 3 Linux servers.

I use the Thecus iSCSI to back off ESX VM servers and ESX clusters the store between all the servers but only for access to the VM images not for share working storage.