Re: configuring new server / many slow disks?

Axel Rau wrote:
> Hi performers,
>
> after following this list for a while, I try to configure a database
> server with a limited budget.
> Planned are 2 databases
> - archiveopteryx - http://www.archiveopteryx.org/sql-schema.html
> - ERDB -
> https://www.chaos1.de/svn-public/repos/network-tools/ERDB/trunk/database/ERD.pdf
>
> In peak times I expect something like
> - 50 inserts
> - 20 updates
> - 200 selects
> per second.

Presumably with multiple clients, not just one extremely busy one?
How big do you expect the databases to get? That'll affect the next point.

> Current configuration is:
> - Tyan S3992G3NR
> - 2 x Opteron 2212 (2GHz)
> - 8 GB RAM (DDR2-667)

Depending on the amount of data you've got to deal with, it might be
worth trading disks/cpu for more RAM.

> - ARC-1261ML with 1GB and BBU

OK, so you can turn write-caching on. That should let you handle more
updates than you need. You probably don't need so much RAM on board
either, unless each update has a lot of data in it.

> - 16 Seagate ST3250820NS (250GB, 7200 rpm, 8GB, with perpendicular
> recording)
>
> 1 raid 1 for OS (FreeBSD) and WAL
> 1 raid 0 with 7 raid 1 for tablespace
>
> Can I expect similar performance as 5 drives at 10k rpm (same costs)?

The main question is whether you're going to need to hit the disks
often. If you can get to the stage where the working-set of your DBs are
all in RAM you could sacrifice some disks. If not, disk I/O dominates.

> Should I revert to a single-CPU to prevent from oscillating cache
> updates between CPUS?
> Anybody experience about NUMA stuff with FreeBSD?

Sorry - I know nothing about FreeBSD.

That any use - I didn't bother to reply before because I couldn't help
with the BSD stuff, and it's always guesswork with these sorts of questions.
--
Richard Huxton
Archonet Ltd