Date: Fri, 17 Sep 2010 22:10:21 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Chris Watson <bsdunix44@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS I/O Throughput question.. Message-ID: <20100917201021.GD1902@garage.freebsd.pl> 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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--hxkXGo8AKqTJ+9QI Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Sep 17, 2010 at 09:35:21PM +0200, Pawel Jakub Dawidek 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 # apply "dd if=3D/dev/zero of=3D/dev/ada%1 bs=3D1m count=3D5000 &" 2 3 4 5 Thanks to se@ for noticing this. > 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 Pawel Jakub Dawidek http://www.wheelsystems.com pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! --hxkXGo8AKqTJ+9QI Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iEYEARECAAYFAkyTyywACgkQForvXbEpPzQNuwCfbYa9OSUjAQQDIfLY2RBnVh9E y2kAn3DdRqbA6PTH3qRYHwe1LoA5WqSy =jbFu -----END PGP SIGNATURE----- --hxkXGo8AKqTJ+9QI--
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