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Re: Tuning PostgreSQL

From: Ron Johnson <ron(dot)l(dot)johnson(at)cox(dot)net>
To: PgSQL Performance ML <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Tuning PostgreSQL
Date: 2003-07-29 15:46:15
Message-ID: 1059493575.7505.129.camel@haggis (view raw or flat)
Thread:
Lists: pgsql-performance
On Tue, 2003-07-29 at 10:14, Vivek Khera wrote:
> >>>>> "GS" == Greg Stark <gsstark(at)mit(dot)edu> writes:
> 
> GS> "scott.marlowe" <scott(dot)marlowe(at)ihs(dot)com> writes:
> 
> GS> But you have to actually test your setup in practice to see if it
> GS> hurts. A big data warehousing system will be faster under RAID5
> GS> than under RAID1+0 because of the extra disks in the
> GS> stripeset. The more disks in the stripeset the more bandwidth you
> GS> get.
> 
> Anyone have ideas on 14 spindles?  I just ordered a disk subsystem
> with 14 high speed (U320 15kRPM) SCSI disks to hook up with a dell
> PERC3/DC controller (only 128MB cache, though).

14 drives on one SCSI card, eh?  I'd be worried about saturating
the bus.

Maybe it's an old rule of thumb, but I would fill a SCSI chain
more than half full.

> My plan was to do RAID10, but I think I'll play with RAID5 again and
> see which gives me the best performance.  Unfortunatly, it is
> difficult to recreate the highly fragmented tables I have now (vacuum
> full takes over 14 hours on one of the tables) so I'm not sure how to
> best compare them.

Also IMO: if I needed something *really* high performance, I'd
start with a mobo that has dual PCI buses (133MB/s can get swamped
quickly by U320 devices) or PCI-X (but they're so new...).

Then:
- get dual U320 SCSI cards (one for each PCI bus) 
- plug them into dual redundant fast path external storage controllers
  that have, oh, 512MB RAM cache *each*)
- dual port the drives, so they plug into both storage controllers

Since I wouldn't put 14 drives on one SCSI chain, double what I
just said, and only plug 7 drives in each controller.

If your app needs One Big Honkin' Device, use the Linux Volume
Manager (LVM) to merge the 2 RAID logical devices into one "super-
logical" device.

Yes, that's lot's of money, but is the data, and speed, important
enough?

-- 
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| Ron Johnson, Jr.        Home: ron(dot)l(dot)johnson(at)cox(dot)net             |
| Jefferson, LA  USA                                              |
|                                                                 |
| "I'm not a vegetarian because I love animals, I'm a vegetarian  |
|  because I hate vegetables!"                                    |
|    unknown                                                      |
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