Re: thin provisioned LUN support

Matthew Wilcox
2008-11-07T20:21:51Z

On Fri, Nov 07, 2008 at 03:19:13PM -0500, Theodore Tso wrote:
> Let's be just a *little* bit fair here. Suppose we wanted to
> implement thin-provisioned disks using devicemapper and LVM; consider
> that LVM uses a default PE size of 4M for some very good reasons.
> Asking filesystems to be a little smarter about allocation policies so
> that we allocate in existing 4M chunks before going onto the next, and
> asking the block layer to pool trim requests to 4M chunks is not
> totally unreasonable.
>
> Array vendors use chunk sizes > than typical filesystem chunk sizes
> for the same reason that LVM does. So to say that this is due to
> purely a "broken firmware architecture" is a little unfair.

I think we would have a full-throated discussion about whether the
right thing to do was to put the tracking in the block layer or in LVM.
Rather similar to what we're doing now, in fact.

--
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."