Re: Best hardware/cost tradoff?

On Thu, Aug 28, 2008 at 3:29 PM, cluster <skrald(at)amossen(dot)dk> wrote:
> Thanks for all your replies! They are enlightening. I have some additional
> questions:
>
> 1) Would you prefer
> a) 5.4k 2" SATA RAID10 on four disks or
> b) 10k 2" SAS RAID1 on two disks?
> (Remember the lots (!) of random reads)

I'd lean towards 4 disks in RAID-10. Better performance when > 1 read
is going on. Similar commit rates to the two 10k drives. Probably
bigger drives too, right? Always nice to have room to work in.

> 2) Should I just make one large partition of my RAID? Does it matter at all?

Probably. With more disks it might be advantageous to split out two
drives into RAID-10 for pg_xlog. with 2 or 4 disks, splitting off two
for pg_xlog might slow down the data partition more than you gain from
a separate pg_xlog drive set.

> 3) Will I gain much by putting the OS on a saparate disk, not included in
> the RAID? (The webserver and database would still share the RAID - but I
> guess the OS will cache my (small) web content in RAM anyway).

The real reason you want your OS on a different set of drives is that
it allows you to reconfigure your underlying RAID array as needed
without having to reinstall the whole OS again. Yeah, logging to
/var/log will eat some bandwidth on your RAID as well, but the ease of
maintenance is why I do it as much as anything. A lot of large
servers support 2 fixed drives for the OS and a lot of removeable
drives hooked up to a RAID controller for this reason.