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Date: Tue, 12 Mar 2002 10:17:07 +0900
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From: GOTO Masanori <gotom@debian.or.jp>
To: garloff@suse.de, dougg@torque.net, sct@redhat.com,
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Subject: Re: [PATCH] 2.4.x write barriers (updated for ext3)
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At Mon, 11 Mar 2002 12:13:00 +0100,
Kurt Garloff <garloff@suse.de> wrote:
> On Sun, Mar 10, 2002 at 12:24:12AM -0500, Douglas Gilbert wrote:
> > "Stephen C. Tweedie" wrote:
> > > Even if WCE is enabled in the caching mode page, we can still set FUA
> > > (Force Unit Access) in individual write commands to force platter
> > > completion before commands complete.
> > > 
> > > Of course, it's a good question whether this is honoured properly on
> > > all drives.
> > > 
> > > FUA is not available on WRITE6, only WRITE10 or WRITE12 commands.
> > 
> > Stephen,
> [...]
> > 
> > Also SYNCHRONIZE CACHE(10) allows a range of blocks to be sent
> > to the platter but the size of the range is limited to 2**16 - 1
> > blocks which is probably too small to be useful. If the
> > "number of blocks" field is set to 0 then the whole disk cache
> > is flushed to the platter.
> 
> Which I think we should send before shutdown (and possible poweroff) for
> disks (DASDs), Write-Once and Optical Memory devices. (Funny enough, the
> SCSI spec also lists SYNCHRONIZE_CACHE for CD-Rom devices
> Unfortunately, SYNCHRONIZE CACHE is optional, so we would need to ignore any
> errors returned by this command.

I agree.
BTW, power management like suspend/resume needs 
SYNCHRONIZE_CACHE for the broken HDD/controller...?

-- gotom
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