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Date: Sun, 15 Jul 2001 10:44:28 -0700
To: Chris Wedgwood <cw@f00f.org>
From: Jonathan Lundell <jlundell@pobox.com>
Subject: Re: [PATCH] 64 bit scsi read/write
Cc: Daniel Phillips <phillips@bonn-fries.net>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Andrew Morton <andrewm@uow.edu.au>,
        Andreas Dilger <adilger@turbolinux.com>,
        "Albert D. Cahalan" <acahalan@cs.uml.edu>,
        Ben LaHaise <bcrl@redhat.com>,
        Ragnar Kjxrstad <kernel@ragnark.vestdata.no>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        mike@bigstorage.com, kevin@bigstorage.com, linux-lvm@sistina.com
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At 3:22 AM +1200 2001-07-16, Chris Wedgwood wrote:
>On Sun, Jul 15, 2001 at 08:06:39AM -0700, Jonathan Lundell wrote:
>
>     At first glance, by the way, the only write barrier I see in the
>     SCSI command set is the synchronize-cache command, which completes
>     only after all the drive's dirty buffers are written out. Of
>     course, without write caching, it's not an issue.
>
>Is the spec you have distributable? I believe some of the early drafts
>were, but the final spec isn't.
>
>I'd really like to check it out myself, I alwasy assumed SCSI had the
>smarts for write-barriers and force-unit-access but I guess I was
>wrong.
>
>Anyhow, I'd like to see the spec for myself if it is something I can
>get hold of.

I was referring to IBM's spec, as implemented in their recent SCSI 
and FC drives. You can find a copy at 
http://www.storage.ibm.com/techsup/hddtech/prodspec/ddyf_spi.pdf

WRITE EXTENDED has a bit (FUA) that will let you force that 
particular write to go to disk immediately, independent of write 
caching, but there's no suggestion that it otherwise acts as a write 
barrier for cached writes.

WRITE VERIFY implies a CACHE SYNCHRONIZE, so it's a write barrier, 
but an expensive (because synchronous) one.
-- 
/Jonathan Lundell.
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