On Sat, May 14, 2005 at 01:22:05PM +0400, [EMAIL PROTECTED] wrote: +> +> Hardware: SATA RAID adapter with SiliconImage 3114 chip. 2 SATA HDD. +> I did gmirror. +> +> Run test: +> 3 parallel tasks "dd if=/dev/mirror/gm0 of=/dev/null bs=1m count=5000" +> +> gstat shows summary read speed from mirror about 30-40 mbyte/sec. +> It is for all balance algorithms: load, round-robin, split +> +> While, one "dd if=/dev/ad4 of=/dev/null bs=1m count=5000" shows 50 mbyte/sec +> +> 1. Why it occurs and how fix it ? +> +> 2. If in the test instead of three instancies of "dd if=/dev/mirror/gm0 +> of=/dev/null bs=1m count=5000" run only one, +> then read speed don`t exceeds read speed from one disk (dd if=/dev/ad4 +> of=/dev/null bs=1m count=5000) +> a) This is gmirror feature ? +> b) This is hardware feature (SiliconImage 3114 chip) ?
This is the way RAID1 works. Try to imagine how disk's heads are moving - there will be no speed-up in sequential reads, this is not RAID0. Mirror characteristics are: - the same speed for sequential reads as for one disk; - the same speed for sequential/random write as for one disk; - double speed of one disk for random reads; -- Pawel Jakub Dawidek http://www.wheel.pl [EMAIL PROTECTED] http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am!
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