Over provisioning does not directly increase flash performance, but allows
for greater reliability as the drive ages by improving garbage collection
efforts and reducing write amplification.  This article doesn't provide any
sources, but it explains the concept at a very basic level -

This thread contains quite a bit of testing and analysis regarding
performance of several different SSDs under constant, 100% write workloads.
 Some of the drives have had close to 300TiB of writes and are still kicking
 The tests were all conducted under Windows with TRIM, however, so this
isn't directly applicable to using a SSD for a ZIL.

On Fri, Aug 12, 2011 at 8:53 PM, Edward Ned Harvey <
opensolarisisdeadlongliveopensola...@nedharvey.com> wrote:

> > From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> > boun...@opensolaris.org] On Behalf Of Ray Van Dolson
> >
> > For ZIL, I
> > suppose we could get the 300GB drive and overcommit to 95%!
> What kind of benefit does that offer?  I suppose, if you have a 300G drive
> and the OS can only see 30G of it, then the drive can essentially treat all
> the other 290G as having been TRIM'd implicitly, even if your OS doesn't
> support TRIM.  It is certainly conceivable this could make a big
> difference.
> Have you already tested it?  Anybody?  Or is it still just theoretical
> performance enhancement, compared to using a "normal" sized drive in a
> normal mode?
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