Re: [PATCH] 64 bit scsi read/write

Jonathan Lundell
2001-07-15T17:45:11Z

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.