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>
next in thread | previous in thread | raw e-mail | index | archive | help
I'll be able to test that in 8 hours. Thanks for the reply! I'll post result= s then. Also, what *is* the recommended way to get a more accurate test of f= ile I/O regarding zfs? dd clearly isn't the best tool. Postmark? Blogbench? Chris=20 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 =20= >> question that is perplexing me. Everything I have read on ZFS says in =20= >> almost every case mirroring is faster than raidz. So I initially setup =20= >> a 2x2 Raid 10 striped mirror. Like so: > [...] >=20 > Could you try running something like this: >=20 > # apply "dd if=3D/dev/ada%1 of=3D/dev/null bs=3D1m count=3D5000 &" 2 3 4= 5 >=20 > This will tell us how much of total throughput do you have. > If you can destroy your data, you may also try this: >=20 > # apply "dd if=3D/dev/null of=3D/dev/ada%1 bs=3D1m count=3D5000 &" 2 3 4= 5 >=20 > 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. >=20 > And no, there are neither special RAIDZ optimizations not special mirror > pesimizations in FreeBSD. >=20 > --=20 > Pawel Jakub Dawidek http://www.wheelsystems.com > pjd@FreeBSD.org http://www.FreeBSD.org > FreeBSD committer Am I Evil? Yes, I Am!
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?42855753-ED49-4850-8E9F-DB3DEB984E36>