Disk write caching, hw.ata.wc and atacontrol disagree

Martin Cracauer cracauer at cons.org
Wed Dec 7 14:30:25 PST 2005

Dieter wrote on Wed, Dec 07, 2005 at 02:05:40PM +0000: 
> I'm trying to turn off the evil data corrupting on-disk write cache.
> I added hw.ata.wc=0 to /boot/loader.conf and rebooted.
> # sysctl hw.ata.wc    
> hw.ata.wc: 0
> So far so good.  But! atacontrol cap ad4 says:
> Feature                      Support  Enable    Value           Vendor
> write cache                    yes      yes
> So hw.ata.wc thinks that the disk write cache is off,
> but atacontrol cap thinks the disk write cache is on?

I remember this is working but there was a reporting problem in

You should easily be able to tell whether it is on or off by the write
performance.  It should plummet by a factor of 4 or so.

cstream -i- -o/mnt/wherever/tmpfile -v1

Martin Cracauer <cracauer at cons.org>   http://www.cons.org/cracauer/
FreeBSD - where you want to go, today.      http://www.freebsd.org/

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