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Date: Mon, 18 Jun 2007 14:03:27 -0400 From: lsorense@...lub.uwaterloo.ca (Lennart Sorensen) To: david@...g.hm Cc: Brendan Conoboy <blc@...hat.com>, Neil Brown <neilb@...e.de>, Wakko Warner <wakko@...mx.eu.org>, linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org Subject: Re: limits on raid On Mon, Jun 18, 2007 at 10:28:38AM -0700, david@...g.hm wrote: > I plan to test the different configurations. > > however, if I was saturating the bus with the reconstruct how can I fire > off a dd if=/dev/zero of=/mnt/test and get ~45M/sec whild only slowing the > reconstruct to ~4M/sec? > > I'm putting 10x as much data through the bus at that point, it would seem > to proove that it's not the bus that's saturated. dd 45MB/s from the raid sounds reasonable. If you have 45 drives, doing a resync of raid5 or radi6 should probably involve reading all the disks, and writing new parity data to one drive. So if you are writing 5MB/s, then you are reading 44*5MB/s from the other drives, which is 220MB/s. If your resync drops to 4MB/s when doing dd, then you have 44*4MB/s which is 176MB/s or 44MB/s less read capacity, which surprisingly seems to match the dd speed you are getting. Seems like you are indeed very much saturating a bus somewhere. The numbers certainly agree with that theory. What kind of setup is the drives connected to? -- Len Sorensen - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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