Обсуждение: Re: [PERFORM] best arrangement of 3 disks for (insert) performance

On Sat, 2003-09-13 at 23:44, Cott Lang wrote:
> > Having WAL on a separate drive from the database would be something of
> > a win.  I'd buy that 1 disk for OS+WAL and then RAID [something]
> > across the other two drives for the database would be pretty helpful.
>
> Just my .02,
>
> I did a lot of testing before I deployed our ~50GB postgresql databases
> with various combinations of 6 15k SCSI drives. I did custom benchmarks
> to simulate our applications, I downloaded several benchmarks, etc.
>
> It might be a fluke, but I never got better performance with WALs on a
> different disk than I did with all 6 disks in a 0+1 configuration.
> Obviously that's not an option with 3 disks. =)

Interesting.  Where did you put the OS, and what kind of, and how
many, SCSI controllers did you have?

PCI 32bit/33MHz or 64bit/66MHz PCI?  32bit/33MHz PCI has a max
throughput of 132MB/s, which is 60% smaller than the theoretical
bandwidth of U320 SCSI, so maybe you were saturating the PCI bus,
and that's why a separate WAL didn't show any improvement?

(If the WAL ever becomes the vehicle for PITR, then it will have
to be on a separate disk [and preferably a separate controller],
even if it slows performance.)

--
-----------------------------------------------------------------
Ron Johnson, Jr. ron.l.johnson@cox.net
Jefferson, LA USA

"Eternal vigilance is the price of liberty: power is ever
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Wendell Phillips

On Mon, 2003-09-15 at 01:05, Ron Johnson wrote:

> Interesting.  Where did you put the OS, and what kind of, and how
> many, SCSI controllers did you have?

I ended up with the OS on the same volume, since it didn't seem to make
any difference.  I'm using a SuperMicro 6023P chassis with an Adaptec
2010S ZCR controller (64bit/66mhz).

I wouldn't recommend SuperMicro to anyone else at this point because
instead of hooking up both U320 channels to the 6 drive backplane, they
only hook up one.  Half the bandwidth, no redundancy. I already had a
burp on the SCSI channel during a single drive death take out one box.
:(

> (If the WAL ever becomes the vehicle for PITR, then it will have
> to be on a separate disk [and preferably a separate controller],
> even if it slows performance.)

Well, it won't have to... but it's certainly a good idea. :)

If we ever get PITR, I'll be so happy I won't mind rebuilding my boxes,
and hopefully I'll have a better budget at that point. ;^)

BTW, I didn't get WORSE performance with the WALs on separate disks, it
just wasn't any better. Unfortunately I lost the spreadsheet I had all
my results in, so I can't be any more specific.