Re: thin provisioned LUN support & file system allocation policy

Matthew Wilcox
2008-11-07T14:34:27Z

On Fri, Nov 07, 2008 at 09:26:49AM -0500, Ric Wheeler wrote:
> One more consideration that I should have mentioned is that we can also
> make our file system allocation policies "thin provisioned LUN" friendly.
>
> Basically, we need to try to re-allocate blocks instead of letting the
> allocations happily progress across the entire block range. This might
> be the inverse of an SSD friendly allocation policy, but would seem to
> be fairly trivial to implement :-)

It's the opposite of a _flash_ friendly policy. But SSDs are not naive
flash implementations -- if you overwrite a block, it'll just write
elsewhere and update its internal mapping of LBAs to sectors. I
honestly think there's no difference in performance between overwriting
a block and writing elsewhere ... as long as you TRIM the LBAs you're no
longer using, of course ;-)

--
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."