Disabling write-behind on IDE drives, and SMART

[Kevin Oberman]

> Date: Fri, 21 Jan 2005 20:53:12 +1300
> From: Mark Kirkwood <markir at paradise.net.nz>
> Sender: owner-freebsd-stable at freebsd.org
> 
> Jim C. Nasby wrote:
> > Question one: how do I disable write caching on IDE drives? I know the
> > setting is hw.ata.wc=0, but where do I put that? In loader.conf? This is
> > FreeBSD 4.10, btw.
> >
> In /boot/loader.conf will do it.
> 
> > Also, has any thought been given to making the default 0, like it is for
> > SCSI devices? I'm honestly surprised and disappointed that the default
> > is speed over data integrity.
> I think it was trialled in 4.3 then changed for 4.4 (according to the 
> handbook, the performance hit was considered to be too high)

Having been involved in the 4.x flip-flop, the performance cost on some
systems can be HUGE! Backing up my laptop (40 GB) went from 40 minutes
to five hours when the write cache was turned off. 

On the other hand, it is a real risk, especially when combined with
softupdates. For servers that lack solid backup power (not a 10 minute
UPS), I would probably turn it off. But for most systems it is probably
worth the risks.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634