Date: Fri, 19 Dec 2008 02:57:27 -0600 From: "James R. Van Artsdalen" <james-freebsd-fs2@jrv.org> To: Matt Simerson <matt@corp.spry.com> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS performance gains real or imaginary? Message-ID: <494B61F7.3030904@jrv.org> In-Reply-To: <D18EBA53-704F-4C21-9BF9-CDBB2AF918D2@corp.spry.com> References: <22C8092E-210F-4E91-AA09-CFD38966975C@spry.com> <alpine.BSF.2.00.0812181732440.14585@ibyngvyr.purzvxnyf.bet> <D18EBA53-704F-4C21-9BF9-CDBB2AF918D2@corp.spry.com>
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Matt Simerson wrote: > I haven't benchmarked it with -HEAD but with FreeBSD 7, using a ZFS > mirror across two 12-disk hardware RAID arrays (Areca 1231ML) was > significantly (not quite double) faster than using JBOD and raidz. I > tested a few variations (four disk pools, six disk zpools, 8 disk > zpools, etc). A backup server is a *highly* specialized type of server. It's likely that data is only rarely updated, meaning that there are very few partial parity-stripe writes for the Areca to deal with. A database server receiving many updates would have an entirely different pattern of write I/O, possibly forcing many partial stripe updates. Since ZFS (almost?) never does partial stripe writes in a RAIDZ the performance comparison between ZFS with JBOD and your hardware setup might change considerably with a database workload. Not to mention the dominance of sequential I/O in a backup server, etc. For a backup server ZFS has other advantages. A client's backup server recently ran low on space so I took over another 4x1GB enclosure and added it to the pool with no downtime: there were a couple of large file writes to that pool running when I arrived that were still going when I left. There's also the issue of cost: once SATA port multiplier support works in FreeBSD it will be very practical to build cheap ~15TB servers for a small business using ZFS.
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