Date: Thu, 11 Jul 1996 10:23:49 -0500 (CDT) From: dnelson@emsphone.com (Dan Nelson) To: mark@plato.ucsalf.ac.uk (Mark Powell) Cc: freebsd-questions@freebsd.org Subject: Re: Does Adaptec 7880 Ultra support simultaneous wide and narrow transfers? Message-ID: <199607111523.KAA22761@dan.emsphone.com> In-Reply-To: <m0ueHpV-00036wC@viking.ucsalf.ac.uk> from "Mark Powell" at Jul 11, 96 10:14:32 am
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in the last episode, Mark Powell said: > > [...] > I assumed that I could simply copy all the data over with > (narrow on sd0, wide on sd1; with 512k on board data buffer): > > $ dd if=/dev/sd0c of=/dev/sd1c bs=512k > > However, this only yields data transfer rates in the 200K/s range. > I've tried both larger and smaller buffer sizes with no apparent > increase. I'm beginning to wonder if the 7870 chipset is performing > these transfers simultaneously. I would expect such a command to push > both drives at full speed with the drive access lights on solidly. > However, the drive lights are alternating off/no for around 1 sec. > periods. Am I expecting the wrong thing here? If I turn on WIDE > negotiation for the W drive, the kernel enables 16bit transfers: What you're telling dd to do is read 512k, write 512k, read 512k, write 512k, etc. That's the cause of your alternating drive lights. Try piping two dd's together, like this: dd if=/dev/sd0c bs=32768 | dd of=/dev/sd1c bs=32768 This will take advantage of the pipe's buffering to let you read and write simultaneously. You may get better results by putting a team command (from /usr/ports/misc) inbetween the two dd's, but that may be overkill. The pipe should be enough. -Dan Nelson dnelson@emsphone.com
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