Re: Hosting a data file on a SAN

On Fri, 28 Feb 2003, victor moran wrote:

> Hello list,
>
> Can someone here help me find out whether or not I can run postgresql 7.2.3
> while keeping its data files on a SAN device across a Fibre Channel link?
>
> I've tried searching for help on Google but when I put SAN into google I get
> too many unrelated hits for unrelated stuff like San Francisco and San Diego.
>
> Any documents or a link to the appropriate manual (so that I can RTFM) would be
> appreciated.

You can. On my main machine I use a pair of local UW scsi drives, but
using the initlocale stuff in postgresql I've setup store on our network
attached storage and had it work quite reliably, and it's not bad on
performance either.

That said, storing your data on a SAN/NAS presents some issues.

(If someone else is reading and doesn't know what they mean:
NAS=Network Attached Storage, SAN = Storage Area Network)

1: What if you don't have NFS / Samba set up right? A problem there
could cause you to lose data.

2: Snapshots on many NAS systems are stored on the same partition as the
data, basically cutting your storage by 50% or even more if multiple snap
shots are stored. A database that changes a lot of data in it may find
that it is using all of the storage on a NAS set up this way. Make sure
snapshots are stored elsewhere if that's an option.

3: Some NAS machines have a slight delay when snapshotting, ours is about
a half a second. No big deal for postgresql, but it sure caused some
issues for Linux at first. RH Linux 7.2 would drop the drive for about 5
minutes after about 1 in every 10 snapshots. We had to change our NFS
options to make it work right.