What is the purpose of a SAN? Is it essential?

[KatanaDV20]

Hows it goin guys

Could you lot pls explain what the purpose of a SAN is? Ive read the Wikki on it but TBH dont get it at all

http://en.wikipedia.org/wiki/Storage_area_network

What is the purpose of it? If youve got server racks etc (and of course these have their own HDs) why would you need one of these SANs? Wont the RAID configs in the servers etc. cater to any backup/traffic needs?

Or is the SAN some kinda isolated backup solution? Is it a kind of uber-NAS?

As you can guess Im lost on this one so totally lookin forward to your replies

Thanks loads!!

 

[rpstewart]

The idea of a SAN is that the individual servers don't have local disk or only have the OS on local disk.

There are plenty of reasons for doing this:

- Space can be added from a shared pool dynamically and in smaller/larger portions than would be available with local disk
- Storage can be shared between clustered servers in an HA environment
- Enterprise SANs have extensive managability features which are simply not available with local disk, flash copy backups for example

 

[shine]

In addition to the reasons above SAN's have some of the fastest and most reliable drives in them couple with five connections for very fast connections to servers.

 

[memyselfandi]

It should be remembered that on top of what has been mentioned above the SAN is a storage network. By that I don't mean a NAS connected to a normal network by a bit of cat5, I mean a full fibre network with storage switches running at 1/2/4/8Gbps. Combined with a cache on enterprise grade disk arrays which could number in the 10's of gigabytes leads to storage which is resilient (multiple paths to disks, disks in raid groups at the array level) and very fast.

A SAN also may have fibre attached tape libraries which can be used to quickly backup the large amounts of data involved.

Replication can be performed at the array level. This can be snapshots, which can then be mounted on to another server and used to create backups without extended outages on the source machine, or it could be an array to array replication in another data centre for site DR purposes (note to any Solution Architects out there ... doing this for Linux boot luns isn't as trivial as you normally think as the WWID of the lun has changed on the replicated copy so some configuration has to be done to be able to boot it at the second site ... don't just assume you can boot it straight away ).