Subject: Re: Low AAC performance but only when tested through the file system
To: Jason Thorpe <>
From: Olaf Seibert <>
List: current-users
Date: 12/04/2003 14:02:53
On Mon 01 Dec 2003 at 22:13:11 -0800, Jason Thorpe wrote:
> You could probably get some improvement by tweaking your stripe depth 
> on the card.  You really want to be writing an entire stripe at a time, 
> so setting your stripe depth to (64k / ndisks-1) for RAID-5 should do 
> the trick (64k because that is the maximum I/O size the NetBSD kernel 
> will currently issue).

> NetBSD really needs to do some work tuning the file system to play nice 
> with RAID.  In particular, tweaking the file system layout for the RAID 
> layout, and making sure to issue I/O that is stripe-aligned and 
> multiple-of-stripe-size would really improve the performance of the 
> file system on RAID-4 and RAID-5.

So, I did some further experiments yesterday. I changed two things, each
of which should improve the performance: I changed the stripe size to
16K, and I changed the geometry in the disklabel to 64 heads and 64
sectors/track.  This way the partitions, which are "cylinder"-aligned,
ought to be better aligned than in the previous 255x63 arrangement.

Strangely enough, performance was 25% *lower* than before! It got only
45 xfers/second, corresponding to about 3 M/sec write speed in bonnie++.

Also, due to differences between BIOS geometry and NetBSD geometry, I
managed to make the disk unbootable.... (except via a boot floppy).

>          -- Jason R. Thorpe <>

___ Olaf 'Rhialto' Seibert - rhialto@       -- "What good is a Ring of Power
\X/            -- if you're Speak." - Agent Elrond