Re: CAM Shingled Disk support patches available

From: Kenneth D. Merry <ken_at_FreeBSD.ORG>
Date: Thu, 19 Nov 2015 15:29:42 -0500
On Thu, Nov 19, 2015 at 12:48:41 -0600, Matthew D. Fuller wrote:
> On Wed, Nov 18, 2015 at 12:13:09PM -0500 I heard the voice of
> Kenneth D. Merry, and lo! it spake thus:
> > 
> > Testing and comments are welcome.
> 
> GELI does explicit handling of each BIO type, so will need to be
> updated to pass it through (possibly in the form of inverting the
> default handling?) or it'll just EOPNOTSUPP it, whether the underlying
> layer does or not.  I wouldn't be surprised if there were other geom
> layers that did similar things.
> 
> Not meant to be read as some kind of "you need to"; just a comment on
> a possible [lack of] impact.

You're correct.  For GEOM classes like GELI that don't change the layout on
disk, passing the BIO_ZONE bio through would be the right thing to do.

For those that change the layout (i.e. the lba you write on the virtual
disk doesn't match what goes down to the physical disk), like graid or
gstripe, I think all we really need to do is just make sure they return
EOPNOTSUPP.  If someone wants to modify that code to handle shingled disks,
they can certainly do that.

Ken
-- 
Kenneth Merry
ken_at_FreeBSD.ORG
Received on Thu Nov 19 2015 - 19:29:51 UTC

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