Subject: Re: disks write-back cache
To: Sean Davis <>
From: Manuel Bouyer <>
List: tech-kern
Date: 04/27/2003 16:03:58
On Sun, Apr 27, 2003 at 09:57:11AM -0400, Sean Davis wrote:
> doesn't appear to work. I tried: dkctl wd0 setcache w, and got a:
> pciide1:0:0: lost interrupt
>   type: ata tc_bcount: 0 tc_skip: 0
> and dkctl getcache still reported writeback cache as enabled.

dkctl wd0 setcache w will enable the cache. If it's already enabled, the
drive may fail to handle it.
My drives don't have problems with this.

> according to the dkctl manpage, my usage was incorrect. however, the command
> according to the dkctl manpage to disable writeback cache would be dkctl wd0
> setcache r, but this gives me:
> dkctl: /dev/rwd0d: setcache: Operation not supported

dkctl wd0 setcache none will work.
The driver is a bit too restrictive (in fact it should accept setcache r and
reject setcache none, as the read cache can't be disabled).
I'll fix this.

Manuel Bouyer <>
     NetBSD: 24 ans d'experience feront toujours la difference