Date: Wed, 12 Jun 2013 04:49:37 -0700 From: Jeremy Chadwick <jdc@koitsu.org> To: Mark Felder <feld@feld.me> Cc: freebsd-fs@freebsd.org Subject: Re: An order of magnitude higher IOPS needed with ZFS than UFS Message-ID: <20130612114937.GA13688@icarus.home.lan> In-Reply-To: <op.wykdduw834t2sn@markf.office.supranet.net> References: <51B79023.5020109@fsn.hu> <op.wykdduw834t2sn@markf.office.supranet.net>
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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@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) -- | Jeremy Chadwick jdc@koitsu.org | | UNIX Systems Administrator http://jdc.koitsu.org/ | | Making life hard for others since 1977. PGP 4BD6C0CB |
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