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>
next in thread | previous in thread | raw e-mail | index | archive | help
[-- Attachment #1 --] 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 > > 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 # apply "dd if=/dev/zero of=/dev/ada%1 bs=1m count=5000 &" 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. > > 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! [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iEYEARECAAYFAkyTyywACgkQForvXbEpPzQNuwCfbYa9OSUjAQQDIfLY2RBnVh9E y2kAn3DdRqbA6PTH3qRYHwe1LoA5WqSy =jbFu -----END PGP SIGNATURE-----
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20100917201021.GD1902>