Date: Sat, 11 Sep 2004 16:05:39 +0200 From: Frode Nordahl <frode@nordahl.net> To: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos@DeepCore.dk> Cc: current@freebsd.org Subject: Re: Promise PDC20267 ATA RAID, poor write performance Message-ID: <A9173D32-03FB-11D9-AA63-000A95A9A574@nordahl.net> In-Reply-To: <4142D833.4060802@DeepCore.dk> References: <EC95929E-031F-11D9-AA63-000A95A9A574@nordahl.net> <4142D833.4060802@DeepCore.dk>
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On Sep 11, 2004, at 12:49, S=F8ren Schmidt wrote: >> Doing simple tests show very poor write performance: >> (reboot) >> # dd if=3D/dev/zero of=3Dfill bs=3D1m count=3D2000 >> 2000+0 records in >> 2000+0 records out >> 2097152000 bytes transferred in 588.383886 secs (3564258 bytes/sec) >> (reboot) >> # dd if=3Dfill of=3D/dev/null bs=3D1m >> 2000+0 records in >> 2000+0 records out >> 2097152000 bytes transferred in 68.492015 secs (30618927 bytes/sec) > > The only thing I could think of was if you have WC (write cache)=20 > turned off for some reason which yields this result here: When you say WC, you mean hw.ata.wc, right? It was enabled. I tried to disable it, and things actually got faster. # dd if=3D/dev/zero of=3Dfill bs=3D1m count=3D2000 2000+0 records in 2000+0 records out 2097152000 bytes transferred in 346.250049 secs (6056756 bytes/sec) Maybe there is some timing issues here somewhere, or just flaky cables=20= :-/ I'll test with other cables and disks and get back. atacontrol cap shows that the disk has write cache as well as read=20 ahead enabled, is it possible to tune this using FreeBSD tools? Mvh, Frode > pizzabox# dd if=3D/dev/zero of=3Dfill bs=3D1m count=3D2000 > 2000+0 records in > 2000+0 records out > 2097152000 bytes transferred in 428.874993 secs (4889891 bytes/sec) > > That looks more like your results, but they are also within what I=20 > would expect when not using WC.. > > > -S=F8ren >
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