Date: Wed, 25 Oct 2006 15:50:04 +0200 (CEST) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-stable@FreeBSD.ORG, guido@gvr.org Subject: Re: Gmirror performanc Message-ID: <200610251350.k9PDo442086250@lurza.secnetix.de> In-Reply-To: <20061025132455.GA52157@gvr.gvr.org>
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Guido van Rooij wrote: > Anyway, I created a gm device and a partition. Now the read performance > is not what I'd expect. > I have the partition on two SATA devices on different controlers. > I get around 60MB/s for each disk. I can get that speed from both disks > simultaneously. > Now when I dd from the gm device, I don't get any speed higher than that. That's expected. > I tried with -b split -s <various sizes>, -b round-robin, -b load. > (dd-ing as done with a bs of 1m; I see the transaction size is 128Kb, > unless the split method is used, in which case the transaction size > gies down. When round-robin is used, the transaction size is 128Kb/s, > but the number of transaction per second goes down.). > > I cannot explain why I should not get a higher read speed. Anyone? dd is a sequential, single-threaded operation, so it will only use one disk at a time. It's not really suitable as a benchmark for real-world things. In the real world [TM] you have multiple processes that access the file system at random. Here you will benefit from the mirror, because accesses will be distributed among the disks. Best regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd Any opinions expressed in this message may be personal to the author and may not necessarily reflect the opinions of secnetix in any way. "anyone new to programming should be kept as far from C++ as possible; actually showing the stuff should be considered a criminal offence" -- Jacek Generowicz
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