Date: Tue, 22 Apr 2008 16:02:00 +1000 From: Andrew Snow <andrew@modulus.org> To: Pete French <petefrench@ticketswitch.com>, freebsd-stable@freebsd.org Subject: Re: Dreadful gmirror performance, though each half works fine Message-ID: <480D7F58.1080203@modulus.org> In-Reply-To: <E1JnuQf-000LaE-5n@dilbert.ticketswitch.com> References: <E1JnuQf-000LaE-5n@dilbert.ticketswitch.com>
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Pete French wrote: > I did some benchmarking, and "load" gives me a bit better performance than > "round-robin" so I've elected to use that. Haven't tried "prefer" as > syncing all the drives backwards and forwards to get the preferences set > seems a bit too much like hard work! I use this patch for sbin/geom/class/mirror/geom_mirror.c Change: md.md_priority = i - 1; To: md.md_priority = i - 1 + 100; This makes the first disk with a priority of 100 instead of 0, which makes it much easier to use "prefer" properly. > It's frustrating, it is *so* close to being workable with iscsi, and the > performance is very good, but if it is going to keep locking up on > me then I just cant use it that way :-( After failing many times with iSCSI, I use geom_gate with the following ggatec options: -t 30 -q 32768 -R 262144 -S 262144 -o rw It seems to be very reliable and fast, but you have to use "prefer" to get good performance, I only write across the network and not read. Load and round-robin lead to slow reads during periods of heavy writes. Hope that helps, - Andrew
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