Re: Tuning PostgreSQL

Hi all,

Vincent, You said that using RAID1, you don't have real redundancy. But
RAID1 is mirroring, right? So if one of the two disks should fail, there
should be no data lost, right?

I have been thinking some more. 18Gb drives are cheaper than 36 or 72Gb
drives. I don't know if I can get the money for this, but how would the
following setup sound?

Two 18Gb (15.000rpm) disks in RAID1 array for Operating System + WAL.
Four 18Gb (15.000rpm) disks in RAID5 array for data.

For the same amount of money, I could also get:

Two 36Gb (10.000rpm) disks in RAID1 array for Operating System + WAL.
Five/Six 36Gb (10.000rpm) disks in RAID5 array for data.

Which would be the best of the above? The one with four 15k-rpm disks or the
one with five/six 10k-rpm disks?
Would these configs be better than all disks in one huge RAID5 array? There
are so many possible configs with RAID.......

Kind regards,
Alexander Priem.

----- Original Message -----
From: "Vincent van Leeuwen" <pgsql(dot)spam(at)vinz(dot)nl>
To: <pgsql-performance(at)postgresql(dot)org>
Sent: Monday, July 21, 2003 6:28 PM
Subject: Re: [PERFORM] Tuning PostgreSQL

> On 2003-07-21 09:06:10 -0700, Josh Berkus wrote:
> > Alexander,
> >
> > > Hmmm. Seems to me that this setup would be better than one RAID5 with
three
> > > 36Gb disks, wouldn't you think so? With one RAID5 array, I would still
have
> > > the data and the WAL on one volume...
> >
> > Definitely. As I've said, my experience with RAID5 is that with less
than 5
> > disks, it performs around 40% of a single scsi disk for large read-write
> > operation on Postgres.
> >
> > If you have only 3 disks, I'd advocate one disk for WAL and one RAID 1
array
> > for the database.
> >
>
> In this setup your database is still screwed if a single disk (the WAL
disk)
> stops working. You'll have to revert to your last backup if this happens.
The
> RAID-1 redundancy on your data disks buys you almost nothing: marginally
> better performance and no real redundancy should a single disk fail.
>
> I'd use RAID-5 if you absolutely cannot use more disks, but I would use
> RAID-10 or two RAID-1 partitions if you can afford to use 4 disks.
>
> Vincent van Leeuwen
> Media Design - http://www.mediadesign.nl/
>
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