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
atacontrol.
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
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Martin Cracauer <cracauer at cons.org> http://www.cons.org/cracauer/
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