Message-ID: <42A008AD.7010307@streppone.it>
Date: Fri, 03 Jun 2005 09:37:17 +0200
From: Cosimo Streppone <cosimo@streppone.it>
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To: Stacy White <harsh@computer.org>
Cc: Postgresql Performance list <pgsql-performance@postgresql.org>
Subject: Re: Adaptec/LSI/?? RAID
References: <002601c56725$2bdd2010$0200a8c0@grownups>
In-Reply-To: <002601c56725$2bdd2010$0200a8c0@grownups>
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Stacy White wrote:

> We're in the process of buying another Opteron server to run Postgres, and
> based on the suggestions in this list I've asked our IT director to get an
> LSI MegaRaid controller rather than one of the Adaptecs.
> 
> But when we tried to place our order, our vendor (Penguin Computing) advised
> "we find LSI does not work well with 4GB of RAM. Our engineering find that
> LSI card could cause system crashes. One of our customer ... has found that
> Adaptec cards works well on PostGres SQL

Probably, your vendor is trying to avoid problems at all, but
"one of our customers" is not a pretty general case, and
"we find LSI does not work well", but is there a documented reason?

Anyway, my personal experience has been with an Acer Altos R701 + S300
external storage unit, equipped with LSI Logic Megaraid U320 aka
AMI Megaraid aka LSI Elite 1600
(honestly, these cards come with zillions of names and subnames, that
I don't know exactly how to call them).

This system was configured in various ways. The final layout is
3 x RAID1 arrays (each of 2 disks) and 1 x RAID10 array (12 disks).
This configuration is only available when you use 2 LSI cards (one
for each S300 scsi bus).

The system behaves pretty well, with a sustained sequential write rate
of 80Mb/s, and more importantly, a quite high load in our environment
of 10 oltp transactions per second, without any problems and
`cat /proc/loadavg` < 1.

I don't like the raid configuration system of LSI, that is
counter-intuitive for raid 10 arrays. It got me 4 hours and
a tech support call to figure out how to do it right.

Also, I think LSI cards don't behave well with particular
raid configurations, like RAID 0 with 4 disks, or RAID 10
with also 4 disks. It seemed that these configurations put
the controller under heavy load, thus behaving unreasonably
worse than, for example, 6-disks-RAID0 or 6-disks-RAID1.
Sorry, I can't be more "scientific" on this.

For Adaptec, I don't have any direct experience.

-- 
Cosimo