Re: Upgrading my BSDI box, again

Bruce Momjian wrote:
> Andrew Sullivan wrote:
> > On Wed, Jul 30, 2003 at 12:38:54AM -0400, Bruce Momjian wrote:
> > > Guys, I just replied to this email on the BSDi email list. The issue is
> > > that someone found that some(most?) IDE drives have write cache enabled,
> > > though the drives do not preserve the write cache data on power failure.
> >
> > It's yet worse than this. Some IDE drives will respond to the
> > command to turn off write cacheing, but they _don't actually turn it
> > off_. In other words, you think you've done the right thing, and you
> > haven't anyway.

> Is there an interface to control this with IDE drives? I know there
> is scsicmd for SCSI, but I didn't think IDE had any similar
> interface to control the drive.

On Linux, there's something called "hdparm." There could be something
analogous, but that misses Andrew's point.

The point is that even if you have a utility that can modify caching
parameters, this is increasingly unlikely to do you any good, because
the hard drive may be lying to you.

The drive happily reports back "Yup! I shut the cache off for you!"

But then proceeds to cache writes anyways, because it was lying when
it said it shut it off.

What OS you're using is irrelevant if the hardware is lying to you.
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Christopher Browne
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