Date: Tue, 21 Jul 2009 07:50:07 GMT From: freebsdpr <freebsdpr@satin.sensation.net.au> To: freebsd-geom@FreeBSD.org Subject: Re: kern/113885: [gmirror] [patch] improved gmirror balance algorithm Message-ID: <200907210750.n6L7o7MC000583@freefall.freebsd.org>
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The following reply was made to PR kern/113885; it has been noted by GNATS. From: freebsdpr <freebsdpr@satin.sensation.net.au> To: bug-followup@FreeBSD.org Cc: freebsdpr <freebsdpr@sensation.net.au> Subject: Re: kern/113885: [gmirror] [patch] improved gmirror balance algorithm Date: Tue, 21 Jul 2009 17:45:37 +1000 (EST) I was also surprised to discover that gmirror, regardless of the algorithm used, does not seem to offer either random or sequential read performance any better than a single drive. I have a new SATA backplane which shows individual drive activity indicators - with these you can easily see that the "load" algorithm seems to be selecting (and staying on) only a single drive at a time, for anywhere between 0.1 - 1 seconds. Some simple testing confirmed that there's no discernable read performance benefit between 1 or >1 drives - so much for my 4 drive RAID1 idea! In comparison, a 5 drive graid3 array offers a sequential read speed of nearly 4 times a single drive... with read verify ON. ---- Onto the "load" patch above - it doesn't seem to work for me. I thought it may have been because I had 4 drives in the array, but even after dropping back to 2 it still only reads from a *single* drive. Any ideas? I'm using 7.1R-amd64. Geom name: db0 State: COMPLETE Components: 2 Balance: load <--- ***
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