Re: Tuning PostgreSQL

On Tue, 2003-07-29 at 10:14, Vivek Khera wrote:
> >>>>> "GS" == Greg Stark <gsstark@mit.edu> writes:
>
> GS> "scott.marlowe" <scott.marlowe@ihs.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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