Date: Fri, 17 Sep 2010 21:35:21 +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: <20100917193521.GC1902@garage.freebsd.pl> In-Reply-To: <82EA2358-F5E5-4CEE-91AC-4211C04F22FD@gmail.com> References: <82EA2358-F5E5-4CEE-91AC-4211C04F22FD@gmail.com>
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--Bu8it7iiRSEf40bY Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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: [...] Could you try running something like this: # apply "dd if=3D/dev/ada%1 of=3D/dev/null bs=3D1m count=3D5000 &" 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=3D/dev/null of=3D/dev/ada%1 bs=3D1m count=3D5000 &" 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. --=20 Pawel Jakub Dawidek http://www.wheelsystems.com pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! --Bu8it7iiRSEf40bY Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iEYEARECAAYFAkyTwvgACgkQForvXbEpPzQInwCgqQ/Xo425FBWSH9tua2Da+tpr uWwAn1XeNmFtTtJJfbk9f9o4CGBm2Il2 =RUn9 -----END PGP SIGNATURE----- --Bu8it7iiRSEf40bY--
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