Re: thin provisioned LUN support

[Ric Wheeler <rwheeler@redhat.com>]

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).

Ric