Date: Sun, 2 Oct 2005 10:04:46 -0700 (PDT) From: Arne "Wörner" <arne_woerner@yahoo.com> To: Patrick Proniewski <patpro@patpro.net> Cc: freebsd-performance@freebsd.org Subject: Re: dd(1) performance when copiing a disk to another Message-ID: <20051002170446.78674.qmail@web30303.mail.mud.yahoo.com> In-Reply-To: <BA9E66B6-BEAE-47F5-A8BA-08686C24CF1F@patpro.net>
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Hi! --- Patrick Proniewski <patpro@patpro.net> wrote: > > Can u find out, if DMA transfers are enabled for those discs? > > What does dmesg say? > > see end of mail for full dmesg output, > Looks good... :-)) But I never saw FBSD's kernel messages about SATA drives... ;-) > > Maybe atacontrol(8) says something useful about SATA discs, > > too (e. g. atacontrol mode 0)? > > # atacontrol mode 0 > Master = BIOSPIO > Slave = BIOSPIO > Hmm... 0 seems to be the wrong ata... Thats why the output does not fit to SATA drives, I think... > # dd if=/dev/ad4 of=/dev/null bs=1m count=1000 > 1000+0 records in > 1000+0 records out > 1048576000 bytes transferred in 17.647464 secs (59417943 > bytes/sec) > That seems to be 2 or about 2 times faster than disc->disc transfer... But still slower, than I would have expected... SATA150 sounds like the drive can do 150MB/sec... As far as I know, SATA busses are independant from each other (no master/slave; every drive gets its own cable)... Maybe "dd" cannot issue a read request, while the write isn't completed? DMA shouldn't be the problem, since the memory interface is quite fast in your case... So there remain the questions: 1. Why does the read speed drop in ur setting (maybe writing to ad6 takes more time than reading from ad4? u could try to run two dd processes one with if=ad4 and the other with if=ad6)? 2. Why can't we reach 150MB/sec? > > (Maybe you could find a way to copy /dev/zero to /dev/ad6 > > without destroying the previous work... :-)) > > well, not very easy both disk are the same size ;) > I thought of the first 1000 1MB blocks... :-) The write speed might be interesting... -Arne __________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.com
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