Date: Mon, 7 Oct 2002 11:12:55 +0930 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Vallo Kallaste <kalts@estpak.ee>, Lars Eggert <larse@ISI.EDU>, Poul-Henning Kamp <phk@critter.freebsd.dk>, n0go013 <ttz@blahdeblah.demon.co.uk>, current <freebsd-current@FreeBSD.ORG> Subject: ccd performance (was: [ GEOM tests ] vinum drives lost) Message-ID: <20021007014255.GC93490@wantadilla.lemis.com> In-Reply-To: <200210061830.g96IUGNF043142@apollo.backplane.com> References: <62515.1033758160@critter.freebsd.dk> <3D9DEFF7.7050508@isi.edu> <20021005125505.GA1248@tiiu.internal> <20021005221456.GR83766@wantadilla.lemis.com> <20021006072155.GA1117@tiiu.internal> <200210061830.g96IUGNF043142@apollo.backplane.com>
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On Sunday, 6 October 2002 at 11:30:16 -0700, Matthew Dillon wrote: > Yes, ccd is fairly light weight. 'man tuning' and 'man ccd' has > a lot of information on how to use it. I generally recommend > using a stripe size of 1152 for multitasking loads. Sectors? Why particularly this value? > Only use a small/tiny stripe size if you need single-tasking > sequential performance (and even then you can take tune the > stripe to the drive's own caching capability). > > The biggest mistake most people make when using striping is that > they use too small a stripe size which causes nearly every read() or > write() to have to be split across multiple drives, which multiplies > the overhead, or causes sequential reads of medium sized files to > constantly seek multiple drives, destroying the effectiveness of having > two seekable heads in the first place. Pretty much exactly what I preach. One disadvantage of large stripes is that they require careful coding to optimize. I haven't looked at ccd, but I know a lot of cheap hardware RAID arrays always read an entire stripe at a time, which requires more memory and takes longer. Have you checked ccd for this? Greg -- See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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