Re: configuring new server / many slow disks?

Am 09.03.2007 um 12:42 schrieb Richard Huxton:

> 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?
Multiple clients do mainly selects (the IMAP users), few mailservers
are busy and do mainly inserts and updates.
> How big do you expect the databases to get?
Up to 1 TB. The 1st DB is an IMAP message store, which keeps Mime
message parts as byteas in one table (bodyparts).

> 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.
updates not, but inserts may have 10-20 MBs.
>
>> - 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.
Because of the table with the blobs, I need the many disks.
Perhaps this table would be worth of on an own table space / raid 10
set.
>
>> 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.
> --
Axel
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