Re: Bad iostat numbers

On Mon, 2006-12-04 at 11:37, Alex Turner wrote:
> The RAID 10 was in there merely for filling in, not really as a
> compare, indeed it would be ludicrous to compare a RAID 1 to a 6 drive
> RAID 10!!
>
> How do I find out if it has version 2 of the driver?

Go to the directory it lives in (on my Fedora Core 2 box, it's in
something like: /lib/modules/2.6.10-1.9_FC2/kernel/drivers/scsi )
and run modinfo on the driver:

modinfo megaraid.ko
author: LSI Logic Corporation
description: LSI Logic MegaRAID driver
license: GPL
version: 2.00.3

SNIPPED extra stuff

> This discussion I think is important, as I think it would be useful
> for this list to have a list of RAID cards that _do_ work well under
> Linux/BSD for people as recommended hardware for Postgresql. So far,
> all I can recommend is what I've found to be good, which is 3ware 9500
> series cards with 10k SATA drives. Throughput was great until you
> reached higher levels of RAID 10 (the bonnie++ mark I posted showed
> write speed is a bit slow). But that doesn't solve the problem for
> SCSI. What cards in the SCSI arena solve the problem optimally? Why
> should we settle for sub-optimal performance in SCSI when there are a
> number of almost optimally performing cards in the SATA world (Areca,
> 3Ware/AMCC, LSI).

Well, I think the LSI works VERY well under linux. And I've always made
it quite clear in my posts that while I find it an acceptable performer,
my main recommendation is based on it's stability, not speed, and that
the Areca and 3Ware cards are generally regarded as faster. And all
three beat the adaptecs which are observed as being rather unstable.

Does this LSI have battery backed cache? Are you testing it under heavy
parallel load versus single threaded to get an idea how it scales with
multiple processes hitting it at once?

Don't get me wrong, I'm a big fan of running tools like bonnie to get a
basic idea of how good the hardware is, but benchmarks that simulate
real production loads are the only ones worth putting your trust in.