Subject: Re: RAID tuning
To: Jukka Marin <firstname.lastname@example.org>
From: Greg Oster <email@example.com>
Date: 12/19/2002 15:20:02
Jukka Marin writes:
> What does the following mean (output from systat):
> Discs wd4 wd5 cd0 wd0 wd1 fd0 md0 raid 64 fmin
> seeks 85 ftarg
> xfers 138 137 128 itarg
> Kbyte 1256 1249 1256 523 wired
> %busy 3.2 2.4 94.4 pdfre
> Why is raid 94.4% busy when the components (wd0, wd1) are only 3%
> busy? CPU is about 90% idle.
> START queue
> fifo 100
> #scan 400
> Someone said I should be using "scan" instead of "fifo" with IDE disks.
> Why is that?
I'd ask the "someone" ;)
> Can I change this parameter without initializing the raid
> set (ie. losing all my data)?
Yes. Note that the queue type (and size) is not stored in the component
labels, so if you're using autoconfig, then it will automatically use fifo,
and you won't be able to change it. (yes, that's a bug, and yes, it's on my
TODO list, and no, there hasn't been a lot (read: any) demand to fix that
bug yet :-} )