Date: Fri, 26 Jul 2002 13:15:28 -0400 (EDT) From: David Miller <dmiller@sparks.net> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: David Gilbert <dgilbert@velocet.ca>, Keith Pitcher <kpitcher@locallink.net>, freebsd-hackers@FreeBSD.ORG Subject: Re: [hackers] Multi CDR burn Message-ID: <Pine.BSF.4.21.0207261253431.98442-100000@search.sparks.net> In-Reply-To: <200207092107.g69L7aOE054059@apollo.backplane.com>
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On Tue, 9 Jul 2002, Matthew Dillon wrote: > > There is no multi-target command that I know of. You are absolutely > correct in your bandwidth calculations... a SCSI bus should have no > problem at all duping the data 8 times to each of 8 CDR's, and the > operating system ought to do a fine job caching the input image file > (so the data is only read off the hard disk once). CDRs are really slow > compared to what a SCSI bus is designed to handle. > > I'm somewhat interested in knowing that this concept actually works :-) The concept works fine, but the numbers are a little off. The actual bandwidth calculations are right, but make the assumption that the max data transfer rate is in effect, without the overhead of connect/disconnect/command queuing. Several years ago I built a DVD-ram duplicatior with FreeBSD. DVD-ram drives, at the time, only came in 10 MB scsi versions, and they took data at about 650Kbit. A single 10 MB scsi channel could not, however, stream data to more than about 5 of them at once. As for the general concept, I can say it works fine. I built a system with nearly 30 DVD-ram drives on 6 separate scsi channels. At first I tried using a utility that would read from the input image (on hard disk) and write it out to all the drives. Bad media gave me fits, Ken Merry was a huge help with the drivers, and in the end it worked fine to just dd the image to all of them. The CPU was an 800 MHz athlon, admittedly much faster than a P-100, but was practically idle when copying to all drives at once. --- David To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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