Date: Fri, 17 Sep 2010 23:41:50 -0500 From: Chris Watson <bsdunix44@gmail.com> To: Pawel Jakub Dawidek <pjd@FreeBSD.org> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS I/O Throughput question.. Message-ID: <B66D903A-3095-4067-81F9-FC17E97E6AE6@gmail.com> In-Reply-To: <20100917201021.GD1902@garage.freebsd.pl> References: <82EA2358-F5E5-4CEE-91AC-4211C04F22FD@gmail.com> <20100917193521.GC1902@garage.freebsd.pl> <20100917201021.GD1902@garage.freebsd.pl>
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priyanka# zpool status pool: tank state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM tank ONLINE 0 0 0 raidz1 ONLINE 0 0 0 ada2 ONLINE 0 0 0 ada3 ONLINE 0 0 0 ada4 ONLINE 0 0 0 ada5 ONLINE 0 0 0 errors: No known data errors priyanka#apply "dd if=/dev/ada%1 of=/dev/null bs=1m count=5000 &" 2 3 4 5 [1] 73068 [1] 73071 [1] 73074 [1] 73077 priyanka# 5000+0 records in 5000+0 records out 5242880000 bytes transferred in 35.093718 secs (149396538 bytes/sec) 5000+0 records in 5000+0 records out 5242880000 bytes transferred in 35.374131 secs (148212262 bytes/sec) 5000+0 records in 5000+0 records out 5242880000 bytes transferred in 36.654998 secs (143033154 bytes/sec) 5000+0 records in 5000+0 records out 5242880000 bytes transferred in 38.558150 secs (135973328 bytes/sec) priyanka# apply "dd if=/dev/zero of=/dev/ada%1 bs=1m count=5000 &" 2 3 4 5 [1] 73130 [1] 73133 [1] 73136 [1] 73139 priyanka# 5000+0 records in 5000+0 records out 5242880000 bytes transferred in 35.149276 secs (149160398 bytes/sec) 5000+0 records in 5000+0 records out 5242880000 bytes transferred in 35.786368 secs (146504949 bytes/sec) 5000+0 records in 5000+0 records out 5242880000 bytes transferred in 36.552717 secs (143433387 bytes/sec) 5000+0 records in 5000+0 records out 5242880000 bytes transferred in 40.162832 secs (130540595 bytes/sec) priyanka# On Sep 17, 2010, at 3:10 PM, Pawel Jakub Dawidek wrote: > 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!
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