the RAID question, again

Hi,

I want to ask the 'which RAID setup is best for PostgreSQL?' question again.
I've read a large portion of the archives of this list, but generally the
answer is 'depends on your needs' with a few different camps.

My needs are as follows: dedicated PostgreSQL server for a website, which does
much more select queries than insert/updates (although, due to a lot of
caching outside the database, we will be doing more updates than usual for a
website).

The machine which will be built for this is going to be something like a dual
Xeon 2.4GHz, 4GB RAM, and a SCSI hardware RAID controller with some cache RAM
and 6-7 36GB 15K rpm disks. We have good experiences with ICP Vortex
controllers, so I'll probably end up buying on of those again (the GDT8514RZ
looks nice: http://www.icp-vortex.com/english/product/pci/rzu320/8514rz_e.htm
)

We normally use Debian linux with a 2.4 kernel, but we're thinking we might
play around with FreeBSD and see how that runs before making the final choice.

The RAID setup I have in my head is as follows:

4 disks for a RAID 10 array, for the PG data area
2 disks for a RAID 1 array, for the OS, swap (it won't swap) and, most
importantly, WAL files
1 disk for hot spare

RAID 1 isn't ideal for a WAL disks because of the (small) write penalty, but
I'm not sure I want to risk losing the WAL files. As far as I know PG doesn't
really like losing them :) This array shouldn't see much I/O outside of the
WAL files, since the OS and PG itself should be completely in RAM when it's
started up.

RAID 5 is more cost-effective for the data storage, but write-performance is
much lower than RAID 10.

The hot-spare is non-negotiable, it has saved my life a number of times ;)

Performance and reliability are the prime concerns for this setup. We normally
run our boxes at extremely high loads because we don't have the budget we
need. Cost is an issue, but since our website is always growing at an insane
pace I'd rather drop some cash on a fast server now and hope to hold out till
the end of this year than having to rush out and buy another mediocre server
in a few months.

Am I on the right track or does anyone have any tips I could use?


On a side note: this box will be bought a few days or weeks from now and
tested during a week or so before we put it in our production environment (if
everything goes well). If anyone is interested in any benchmark results from
it (possibly even FreeBSD vs Linux :)) that can probably be arranged.


Vincent van Leeuwen
Media Design - http://www.mediadesign.nl/