Date: Sun, 5 Aug 2012 16:44:58 +0100 From: Steve O'Hara-Smith <steve@sohara.org> To: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> Cc: freebsd-questions@freebsd.org Subject: Re: ZFS bonnie puzzlement Message-ID: <20120805164458.1c012ac4.steve@sohara.org> In-Reply-To: <alpine.BSF.2.00.1208051327310.21508@wojtek.tensor.gdynia.pl> References: <20120804142758.0126fded.steve@sohara.org> <alpine.BSF.2.00.1208051327310.21508@wojtek.tensor.gdynia.pl>
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On Sun, 5 Aug 2012 13:29:51 +0200 (CEST) Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> wrote: > > are showing me. Read performance OTOH is strange, zpool and systat both > > reporting consistently an aggregated read speed of around 120MB/s during > > the block read tests (which seems a bit slow for the drives - and indeed > > systat reports the drives at less than 50% utilisation) but bonnie is > > only reporting 35MB/s, I see similar discrepancies with simple dd block > > reads to /dev/null, in which case my stopwatch agrees with dd. > no it is not wrong. > > Do more tests (possibly your own doing heavy mixed workload) to > understand well why you should not use this "last word in filesystems". First surprise, with only 4GB I had set primarycache=metadata, changing that to primarycache=all caused the systat, zpool iostat and bonnie figures all to agree - and made them all a bit better too. Lesson from this - don't bother setting primarycache=metadata. With that puzzle gone testing and tuning becomes more useful: Enabling prefetch made a huge difference to the per char sequential read, but didn't really change anything else. Indeed this test is now CPU limited in bonnie - that'll do. Rebooting with zfs.cache_flush_disable=1 made everything faster. Block writes and reads maxed out the discs at around 110MB/s and 200MB/s respectively - pretty close to the raw disc speed. Rewrite nearly doubled in speed too. Next stop NFS tuning. -- Steve O'Hara-Smith | Directable Mirror Arrays C:>WIN | A better way to focus the sun The computer obeys and wins. | licences available see You lose and Bill collects. | http://www.sohara.org/
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