Re: thin provisioned LUN support

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, Nov 07 2008, Ric Wheeler wrote:
> Jens Axboe wrote:
> >On Thu, Nov 06 2008, David Woodhouse wrote:
> >  
> >>On Thu, 6 Nov 2008, James Bottomley wrote:
> >>    
> >>>The way to do this properly would be to run a chequerboard of partials,
> >>>but this would effectively have trim region tracking done in the block
> >>>layer ... is this worth it?
> >>>
> >>>By the way, the latest (from 2 days ago) version of the Thin
> >>>Provisioning proposal is here:
> >>>
> >>>http://www.t10.org/ftp/t10/document.08/08-149r4.pdf
> >>>
> >>>I skimmed it but don't see any update implying that trim might be
> >>>ineffective if we align wrongly ... where is this?
> >>>      
> >>I think we should be content to declare such devices 'broken'.
> >>
> >>They have to keep track of individual sectors _anyway_, and dropping 
> >>information for small discard requests is just careless.
> >>    
> >
> >I agree, seems pretty pointless. Lets let evolution take care of this
> >issue. I have to say I'm surprised that it really IS an issue to begin
> >with, are array firmwares really that silly?
> >
> >It's not that it would be hard to support (and it would eliminate the
> >need to do discard merging in the block layer), but it seems like one of
> >those things that will be of little use in even in the near future.
> >Discard merging should be useful, I have no problem merging something
> >like that.
> >
> >  
> I think that discard merging would be helpful (especially for devices 
> with more reasonable sized unmap chunks).

Indeed, and it fits in well with what we do already. Dave has this
mostly done I think, so 2.6.29 should be a potential target provided
that it gets sent soon :-)

-- 
Jens Axboe