Re: hardware for a server - Mailing list pgsql-general

On Sat, Mar 13, 2010 at 1:34 AM, A B <gentosaker@gmail.com> wrote:
> Hello.
>
> It's time to get new hardware for a server that will run both
> PostgreSQL and Apache.
> The workload will be similar to that of  your standard "PHP forum"
> (most selects and logging of stuff that has been read)
>
> The modell I'm looking at right now is
>
> 2x Xeon E5520 2,26 GHz 8 MB (8 cores in total)
> 24 GB 1066 MHz DDR 3 ECC (or more)
>
> When it comes to a RAID controller I have the choice of:
>
> 3Ware SAS 9690SA-8i 512 MB BBU
> Adaptec SAS Raid 5805  256 MB BBU
> LSI MegaRaid SAS 8708 128 MB BBU
>
> Any advice/experience on what raid controller to pick? The 3ware has
> the most memory and I've read some good reviews on that one.
> The OS will be CentOS 5.4

I can't comment on any of those particular controllers.  There's a
benchmark here:

http://www.tomshardware.com/reviews/adaptec-serial-controllers,1806-11.html


> When it comes to harddrives I think my best optins is to use
>
> * 4 discs (raid 10)  for the database
>
> and
>
> * 4 discs (raid 10) for OS, xlog and other data (images,avatars etc.)
> or more likely:
> * 2 discs (raid 1) for OS/xlog and
> * 2 discs  (raid1) for "other data"

Leaving out 2 drives for other data is kind of a waste of spindles.
You can network mount terabytes from a file server full of SATA drives
for much less.

Also...

> When it comes to choosing the acctual discs I guess this would be
> appropriate to use:
> "other data":  Barracda ES.2 1000 GB (SATA)  to get a a good GB/$ ratio.
> OS/xlog : Barracuda ES.2 500 GB (SAS)
> DB: Cheeta 15K.6  146 GB (SAS) (The 300 GB would be better if I can
> find some more money)

Mixing SATA and SAS drives on the same controller can be problematic.
Some controllers don't behave well when you mix and match.

I'd suggest building an 8 disk  RAID-10 and a single mirror + 6 disk
RAID-10 and testing both configurations.  If you need more storage
look at 300G SAS drives.  Your two bottleneck are likely to be IO
random write ops and / or CPU horsepower, depending on how your web
app is built. You can always buy another $1500 box with hot cpus and a
pair of big SATA drives if you need more CPU horsepower, but beefing
up IO is a lot hard once your db server is in place.

> This of course gives me a headache when it comes to keeping spare discs.
>
> The other option would be to  use OS/xlog and DB on Barracuda ES.2 500
> GB (SAS). I have no idea what that mean to the performance. A lot/
> barely noticable?

The cost diff now on 500 and 1TB drives is too low to bother with 500
and 1TB mixed, just get 1TB.  And I can't really recommend Seagate
ES.2 or 7200.11 drives right now with the failure rates I've been
seeing.

> Any comments, advice on this kind of setup?

If you've got a lot of reads going on be sure to toss memcached into
this equation.