Date: Tue, 06 Nov 2007 15:16:22 +0100 From: "fluffles.net" <bsd@fluffles.net> To: freebsd-current@freebsd.org Cc: Arne Woerner <arne_woerner@yahoo.com> Subject: geom_raid5 inclusion in HEAD? Message-ID: <47307736.9060900@fluffles.net>
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Hello list! I was wondering if and when the excellent geom_raid5 module created by Arne Wörner would be committed to HEAD or releng_7. Right now there's gvinum with RAID5 support and geom_raid3. The latter is nice but only works with a 'strange' number of disks (3,5,9,17,33, etc) and has the disadvantages associated with RAID3 (no parallel access; all disks are involved in one single write operation), while gvinum offers poor RAID5 write performance (~20MB/s in my testings). geom_raid5, on the other hand, offers excellent performance due to write combining, that allows 2-phase requests to be converted into 1-phase requests. This is achieved by waiting for contiguous requests and splitting those into the 'full stripe', meaning: stripesize * ( number_of_disks - 1). This way, no parity information has to be read from any disk since all required data is already in memory. In normal english this means excellent sequential performance. In my own testings i have achieved over 400MB/s of RAID5 write performance using a simple "dd if=/dev/zero of=/dev/raid5/data bs=1m" of at least 10GB worth of data. raidtest benchmarks show that geom_raid5 scales nicely with the number of disks, though ofcourse RAID5's weak point is random write. Considering this project has been around for quite a while, and sister project FreeNAS has been using it for more than a year in their official (stable) branch, i think it should become available in the official FreeBSD distribution as well. I don't know who decides on this, but i would like to get a discussion going on this matter. Looking forward to any replies! Kind regards, Veronica
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