Re: RAID vs. Single Big SCSI Disk

On Thu, Dec 07, 2000 at 06:24:20PM -0800, G. Anthony Reina wrote:
> We have three databases for our scientific research and are getting
> close to filling our 12 Gig partition. My boss thinks that just getting
> a really big (i.e. > 30 Gig) SCSI drive will be cheaper and should do
> nicely. Currently, we only have 4 people accessing the database and
> usually only have 1-2 jobs (e.g. selects, updates, etc.) going at any
> one time (probably a high estimate). The db sits on a Pentium II/400 MHz
> with RedHat 6.0.
>
> Other than mirroring, are there any other advantages (e.g. speed, cost)
> of just getting a RAID controller over, say, a 73 Gig Ultra SCSI Cheetah
> drive (which cost in the neighborhood of $1300).

A RAID can be both faster and more reliable than a single disk.
I say "can" because not all RAID configurations will be.

> Also, can Postgres handle being spread over several disks? I'd think
> that the RAID must control disk spanning, but just want to make sure
> that Postgres would be compatible.

You can spread the data over several disks by moving some of the files
and creating symlinks, or by using striping (software or hardware) or
concatenation (software or hardware).

Your alternatives for software concatenation/striping will depend on
your OS.

Software RAID will neiter be as fast (because there is no cache and
because it's using your main CPU instead of a dedicated one) nor as
reliable (because there is no battery-backup for updates) as a hardware
RAID.

--
Ragnar Kjørstad
Big Storage