Date: Fri, 17 Sep 2010 15:10:09 -0500 From: Christopher Watson <bsdunix44@gmail.com> To: Pawel Jakub Dawidek <pjd@FreeBSD.org> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: ZFS I/O Throughput question.. Message-ID: <42855753-ED49-4850-8E9F-DB3DEB984E36@gmail.com> In-Reply-To: <20100917193521.GC1902@garage.freebsd.pl> References: <82EA2358-F5E5-4CEE-91AC-4211C04F22FD@gmail.com> <20100917193521.GC1902@garage.freebsd.pl>
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I'll be able to test that in 8 hours. Thanks for the reply! I'll post results then. Also, what *is* the recommended way to get a more accurate test of file I/O regarding zfs? dd clearly isn't the best tool. Postmark? Blogbench? Chris Sent from my iPhone On Sep 17, 2010, at 2:35 PM, Pawel Jakub Dawidek <pjd@FreeBSD.org> wrote: > On Wed, Sep 15, 2010 at 03:05:46AM -0500, Chris Watson wrote: >> I have been testing ZFS on a home box now for a few days and I have a >> question that is perplexing me. Everything I have read on ZFS says in >> almost every case mirroring is faster than raidz. So I initially setup >> a 2x2 Raid 10 striped mirror. Like so: > [...] > > Could you try running something like this: > > # apply "dd if=/dev/ada%1 of=/dev/null bs=1m count=5000 &" 2 3 4 5 > > This will tell us how much of total throughput do you have. > If you can destroy your data, you may also try this: > > # apply "dd if=/dev/null of=/dev/ada%1 bs=1m count=5000 &" 2 3 4 5 > > If you disks cannot work at full speed in parallel this might explain > what you're seeing. Mirror send to disk twice as much data as it > receives and RAIDZ sends only 33% more data in four disk case. > > And no, there are neither special RAIDZ optimizations not special mirror > pesimizations in FreeBSD. > > -- > Pawel Jakub Dawidek http://www.wheelsystems.com > pjd@FreeBSD.org http://www.FreeBSD.org > FreeBSD committer Am I Evil? Yes, I Am!
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