Re: Hardware for a database server - Mailing list pgsql-admin

Erwin Brandstetter wrote:
> CPU:
> Single AMD Opteron.
> Opteron, because i plan to migrate to amd64 debian as soon as Debian
> has a stable release.
> Single, because multi-CPU would only make sense if the CPU could ever
> get the bottleneck. But I don't have to fear that, right? No need for a
> dual-cpu setup?
> Should I consider Athlon 64 FX or Athlon 64? I guess socket 940 has
> more future than socket 754, right?

Until Socket 939 is available, the A64FX is the same CPU as an Opteron
1xx. I'd definitely say stick with 940 for server CPUs because 754/939
does not support registered memory. For server, you will want ECC and
registered because unbuffered memory not only takes a performance hit at
high densities but are much more prone to errors and failure.

> Controller / Hard Discs:
> RAID 5 with 4+ discs including a hot spare. But SCSI or SATA?
> I am undecided on this. Until about a year ago, I would have said SCSI,
> period. But I have read of SATA RAIDs for entry-level-servers doing
> quite well and Linux dealing with it ever more smoothly. ([1], [2])
> So I wonder if it is still a good decission to spend 3 times the money
> per gigabyte on SCSI?

SATA still doesn't have TCQ which is a big big big deal for multi-user
databases. It has simple command queueing -- better than nothing -- but
random access will kill your performance. I know this from experience.

The other item is that you will have a hard time finding a SATA
controller with a battery backed cache. This allows you to safely turn
write caching on -- otherwise, a server crash can corrupt your database.

As for RAID5, RAID0+1 runs quite a bit faster but requires more disks
for the same amount of disk space.

> And do 3ware Controllers still have the best driver support under
> Linux?

If you do go SATA, 3ware is pretty much the only choice. I've tried a
few other vendors and their drivers for Linux are absolutely horrid.
E.g. timeouts, crashes, kernel panics.

> Power supply:
> Secured with UPS, auto-shutdown before power fails, so do I need my
> RAID controller battery-backed still?

You'd need a redundant powersupply -- however, you still would not be
protected from OS crashes. E.g. DB half-written, half in OS cache and
kernel locks up -- recipe for corruption.

> RAM:
> As much as the motherboard will bear. 4 GB probably. This seems the
> easyest point to decide on. Correct? DDR SDRAM PC333 or PC400?

Here's a possible reason to go a 2x opteron MB. They usually have double
the memory slots so you could go to 8GB of RAM (without paying the
astronomical amounts for 2GB/4GB DIMMs).

As for the memory type, it's gotta be ECC/registered. ECC/reg DDR333 is
readily available -- 400 is not as this time so expect to pay a premium.