UDMA vs. VIA 82C686B

Raphael Becker rabe at uugrn.org
Fri Jan 2 02:46:56 UTC 2009

Hi all,

I have had some problems with a VIA 82C686B UDMA100 controller with an
attached 2.5" Harddisk (Samsung-foo, 40GB) running 7.1-RELEASE (GENERIC):

UDMA-access is not possible even tough the HDD is able to do (in my
Laptop) and the controller claims to support UDMA100. 

I tried a CF-Card with the same hardware running 6.2 or 6.3-RELEASE with
the same effect: some bad g_vfs-errors.

I got around this problem by adding (at least one of) the lines to 


Is this a known issue? 
Is there a workaround/patch for UDMA on this VIA-chipset?

Do you need more details on it?
It's kind of difficult to get the exact errors, because hw.ata.* seems
to be a read-only ("boot-only") sysctl and I have limited (serial)
access to the box. In case of hw.ata.ata_dma=1 I'm not able to unset
this value in /boot/loader.conf because I cannot write to the disk
because of the udma-errors then. 


Raphael Becker          <rabe at uugrn.org>          http://rabe.uugrn.org/
GnuPG:                E7B2 1D66 3AF2 EDC7 9828  6D7A 9CDA 3E7B 10CA 9F2D
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