Jeremy Chadwick koitsu at FreeBSD.org
Mon Sep 29 13:52:15 UTC 2008

On Sat, Sep 27, 2008 at 05:36:17PM +1000, Peter Jeremy wrote:
> On 2008-Sep-26 23:44:17 -0700, Jeremy Chadwick <koitsu at freebsd.org> wrote:
> >On Fri, Sep 26, 2008 at 10:35:57PM -0700, Derek Kuli??ski wrote:
> >> As far as I know (at least ideally, when write caching is disabled)
> ...
> >FreeBSD atacontrol does not let you toggle such features (although "cap"
> >will show you if feature is available and if it's enabled or not).
> True but it can be disabled via the loader tunable hw.ata.wc (at
> least in theory - apparently some drives don't obey the cache disable
> command to make them look better in benchmarks).

Off-topic, but those who use it will be interested:

hw.ata.wc has always been one of those "why was it done this way?!"
features which has bothered me.  It never made any sense to either
disable or enable WC on all drives, since there's no guarantee the user
will want that.

With that kept in mind, I've submit a PR containing a small kernel
patch, atacontrol patch, and update to the atacontrol man page that
allows toggling of WC via "atacontrol wc <device> on/off".


Now users will have the ability to do "atacontrol wc <device> on",
enabling WC on drives of their choice.  And yes, you can toggle
on/off in real-time, regardless of what hw.ata.wc contains (that
tunable just acts as a default).

| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |

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