Re: thin provisioned LUN support & file system allocation policy

Matthew Wilcox
2008-11-07T15:45:52Z

On Fri, Nov 07, 2008 at 10:36:24AM -0500, Theodore Tso wrote:
> The discussion here has been around Intel-style SSD's, which
> apparently have a log-structured filesystem in the device, such that
> wear leveling is done automatically, and in fact it is *better* for
> these devices if we reuse the same block since then the SSD
> automatically knows that contents at the old location is logically
> "gone". (I don't believe, or at least don't see, why there would be
> any benefit of reusing block ranges versus explicitly using a TRIM
> command to tell the SSD that the old block was no longer being used;
> it should have the same effect as far as the SSD is concerned.)
>
> The one thing which I am somewhat concerned about is whether all SSD's
> will be doing things the Intel way, or whether other SSD's might not

Given that most of my information about how SSDs work comes from a
presentation given by Samsung at the FS/IO storage workshop, I feel
fairly confident all the manufacturers do something very similar with a
log-structured FS internally.

Of course, this probably doesn't apply to the $5 1Gb USB keys that you
get in the conference schwag, but if we start optimising for those,
we've probably already lost.

--
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."