Re: RAID + PostgreSQL?

I have here an Smart Array 6i with 192 MB Battery Backup Write Cache with
several 146 MB U320 SCSI HDs
and I get read/write speed till 120 MB per secound (HP ProLiant DL 380G4)
under Debian Linux with
Kernel 2.4.32 an Postgresql 7.4.13.

Greetings,

-Franz

-----Ursprüngliche Nachricht-----
Von: Alex Turner [mailto:armtuk(at)gmail(dot)com]
Gesendet: Dienstag, 27. Juni 2006 03:50
An: Tony Caduto
Cc: Scott Marlowe; MG; pgsql general
Betreff: Re: [GENERAL] RAID + PostgreSQL?

Compaq RAID controllers are known to be slow under linux.

Alex.

On 6/26/06, Tony Caduto <tony_caduto(at)amsoftwaredesign(dot)com
<mailto:tony_caduto(at)amsoftwaredesign(dot)com> > wrote:

Scott Marlowe wrote:
> On Mon, 2006-06-26 at 08:59, Tony Caduto wrote:
>
>> MG wrote:
>>
>>> Hello,
>>>
>>> we are using PostgreSQL 8.0.3 together with RAID on OpenServer 6.
>>>
>>> When we do a big SELECT-query the whole maschine becomes very very
>>> very slowly or stands.
>>> The maschine has 3 GB RAM, so we suppose it`s the RAID.
>>>
>>> Has anyone some experience with RAID + PostgreSQL?
>>>
>>> Where does PostgreSQL saves his temporary files? Perhaps these are the
>>> reason for the bad performance.
>>>
>>> Greetings
>>>
>>> Michaela
>>>
>> What kind of RAID? I know if you have it set up to mirror it becomes
>> slow as pond water.
>>
>
> I have to say this has NOT been my experience. With a pair of U320
> drives on an LSI-Megaraid with battery backed cache (256M or 512M, not
> sure which it was, it's been a few years) our pg server was noticeable
> faster with a mirror set than with a single IDE drive (with cache
> disabled) on the same machine. And faster than a single SCSI drive with
> no RAID controller as well.
>
>
Hi Scott,

We are just using the compaq hardware SCSI //raid included with the
server and it does not have a
battery backed cache. Actually my test DB running the same queries on a
cheap IDE drive (on a Athlon 2200+ where 50% faster than the compaq
running the mirrored
SCSI drives. The compaq system was also a Dual 2.4 gzh Xeon with 2.5 GB
of memory and the Athlon had 512mb. Some of the performance on the
Athlon could be attributed to the CPU, but mostly the IDE drive just
blew away the mirrored SCSI drive
On the Compaq system setting Fsync to false increased the speed of all
select statements, not just complex ones with sorting.

I didn't set up the hardware, so I don't know if the system admin guy
screwed anything up in the raid setup.

Later,

--
Tony Caduto
AM Software Design
http://www.amsoftwaredesign.com <http://www.amsoftwaredesign.com>
Home of PG Lightning Admin for Postgresql
Your best bet for Postgresql Administration

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