From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Snitzer <snitzer@redhat.com>
Subject: Re: SCSI's heuristics for enabling WRITE SAME still need work [was:
 dm mpath: disable WRITE SAME if it fails]
Date: Tue, 24 Sep 2013 11:15:13 -0400
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To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org, emilne@redhat.com, device-mapper development <dm-devel@redhat.com>, dgilbert@interlog.com

On Tue, Sep 24 2013 at  9:49am -0400,
Martin K. Petersen <martin.petersen@oracle.com> wrote:

> >>>>> "Mike" == Mike Snitzer <snitzer@redhat.com> writes:
> 
> Mike> So are there drives like this?:
> Mike> 1) don't support RSOC
> Mike> 2) do support WRITE SAME
> Mike> 3) do populate VPD page with either WRITE SAME w/ discard bit set
> Mike>    or UNMAP?
> 
> Yes.
> 
> But again, the fundamental issue here is not the drives. It's the
> controller firmware. I am not aware of a single SPI/SAS/FC drive that
> does not support at least WRITE SAME(10).
> 
> For DIX and T10 PI I have a capabilities mask that each HBA driver fills
> out that tells the sd driver what the controller can do. And this is
> combined with whatever the drive reports to figure out whether integrity
> protection can be enabled.
> 
> I have been contemplating doing something similar for "fancy" SCSI
> commands. We could have a flag in the scsi host template that controls
> whether the device supports WRITE SAME, EXTENDED COPY, etc. The
> advantage being that we do the matching at discovery time instead of
> once a WRITE SAME is issued.
> 
> This would also permit HBA drivers to toggle the feature on a per
> instance basis. I.e. if "RAID controller firmware rev is lower than XYZ,
> do not support WRITE SAME".
> 
> I'll do a PoC later today...

Sounds promising, thanks!