On Fri, Aug 12, 2011 at 06:53:22PM -0700, Edward Ned Harvey 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.

Perhaps this is it.  Pulled the recommendation from Intel's Solid-State
Drive 320 Series in Server Storage Applications whitepaper.

Section 4.1:

  A small reduction in an SSD’s usable capacity can provide a large
  increase in random write performance and endurance. 

  All Intel SSDs have more NAND capacity than what is available for
  user data. The unused capacity is called spare capacity. This area is
  reserved for internal operations.  The larger the spare capacity, the
  more efficiently the SSD can perform random write operations and the
  higher the random write performance. 

  On the Intel SSD 320 Series, the spare capacity reserved at the
  factory is 7% to 11% (depending on the SKU) of the full NAND
  capacity. For better random write performance and endurance, the
  spare capacity can be increased by reducing the usable capacity of
  the drive; this process is called over-provisioning.

> 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?

Haven't yet tested it, but hope to shortly.

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