An order of magnitude higher IOPS needed with ZFS than UFS

[Sergey Lobanov]

On Wednesday 12 June 2013, Jeremy Chadwick wrote:
> On Wed, Jun 12, 2013 at 06:40:32AM -0500, Mark Felder wrote:
> > On Tue, 11 Jun 2013 16:01:23 -0500, Attila Nagy <bra at fsn.hu> wrote:
> > >BTW, the file systems are 77-78% full according to df (so ZFS
> > >holds more, because UFS is -m 8).
> > 
> > ZFS write performance can begin to drop pretty badly when you get
> > around 80% full. I've not seen any benchmarks showing an improvement
> > with a very fast and large ZIL or tons of memory, but I'd expect
> > that would help significantly. Just note that you're right at the
> > edge where performance gets impacted.
> 
> Mark, do you have any references for this?  I'd love to learn/read more
> about this engineering/design aspect (I won't say flaw, I'll just say
> aspect) to ZFS, as it's the first I've heard of it.
> 
> The reason I ask: (respectfully, not judgementally) I'm worried you
> might be referring to something that has to do with SSDs and not ZFS,
> specifically SSD wear-levelling performing better with lots of free
> space (i.e. a small FTL map; TRIM helps with this immensely) -- where
> the performance hit tends to begin around the 70-80% mark.  (I can talk
> more about that if asked, but want to make sure the two things aren't
> being mistaken for one another)

http://lists.freebsd.org/pipermail/freebsd-fs/2013-March/016834.html

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