Re: thin provisioned LUN support

[Matthew Wilcox <matthew@wil.cx>]

On Fri, Nov 07, 2008 at 02:44:08PM -0500, jim owens wrote:
> To do that you kind of have to build a filesystem into the
> block layer to persistently store "mapped/unmapped blocks
> in chunk" and then do the "unmap-this-chunk" when a region
> is all unmapped.
> 
> 250 MB per 1TiB 512b sector disk for a simple 1-bit-per-sector
> state.  And that assumes you don't replicate it for safety.
> That is what the array vendors are trying to avoid by pushing
> it off to the OS.

And it's what the OS people are trying to avoid having to incorporate
by pushing back on the array vendors.

> Whoever supports thin provisioning better get their unmapping
> correct because those big customers will be looking for who
> to blame if they don't get all the features.

It's fairly clear that it's the array vendors at fault here.  They've
designed a shitty product and they're trying to get us to compensate.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."