Re: [PATCH] 2.4.x write barriers (updated for ext3)

Kurt Garloff
2002-03-11T11:13:24Z

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Hi Doug,

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.

Regards,
--
Kurt Garloff <garloff@suse.de> Eindhoven, NL
GPG key: See mail header, key servers Linux kernel development
SuSE Linux AG, Nuernberg, DE SCSI, Security

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