Date: Tue, 1 Mar 2016 15:49:27 -0500
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Christoph Hellwig <hch@lst.de>
Cc: trond.myklebust@primarydata.com, linux-nfs@vger.kernel.org
Subject: Re: pNFS SCSI layout support
Message-ID: <20160301204927.GE23792@fieldses.org>
References: <1456752247-6549-1-git-send-email-hch@lst.de>
 <20160301192408.GC23792@fieldses.org>
 <20160301203012.GA6033@lst.de>
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On Tue, Mar 01, 2016 at 09:30:12PM +0100, Christoph Hellwig wrote:
> On Tue, Mar 01, 2016 at 02:24:08PM -0500, J. Bruce Fields wrote:
> > I still wonder whether this is the best behavior.  How about also adding
> > the ability to configure out the block layout?  I think we'd want to be
> > sure it's completely off in production.
> 
> Being able to configure block layout eventually might be useful.  Do
> you simply want separate compile time options?  It's not like a whole
> lot of code will go away, it's mostly just entry points.

Yeah, I wasn't thinking about the size of the code so much as
supportability.

> > Also todo?:
> > 	- wireshark support
> 
> I've mostly stayed clear of wiresharė.

No problem, just noting it so I don't forget.

> > 	- testing, including of fencing and reboot recovery.
> 
> I've done a fair amount of testing, and the interesting part is
> indeed fencing.  The normal path is not very different from the block
> layout driver.
> 
> > 	(And:
> > 	  currently I just share a file between two vm's to use as my
> > 	  shared block device, I guess I'll need to set up a real SCSI
> > 	  target instead.)
> 
> The in-kernel lio target will work just fine.  You can actually export
> that directly to VMs using the vhost_scsi driver, but I've not tried
> that option myself yet.
> 
> > I think there's not any additional documentation required--this is just
> > like block layout but without the need to configure fencing.
> 
> Exactly.
> 
> > (Or do
> > people need to do some additional configuration of the SCSI devices?  Or
> > check the specs on their hardware to make sure it has support for the
> > right features?)
> 
> Yes, the device needs to support persistent reservations.
> 
> I can write up a little blurb on that.

OK, thanks.

--b.