Date: Mon, 29 Jul 2002 15:34:29 -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.4.21.0207291527080.44047-100000@search.sparks.net> In-Reply-To: <200207291845.g6TIjXAo055731@apollo.backplane.com>
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On Mon, 29 Jul 2002, Matthew Dillon wrote: > :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 > > That's very interesting! Effectively you have a 'buffer' which is > nearly all of physical memory as the kernel caches the file data you > are reading (so only the first dd to request a particular sector actually > has to read it from disk). As long as the various DVDs being written > too do not drift apart more then the size of the cache the data would > only have to be read from the hard disk once. So then it just comes down > to PCI and SCSI bus bandwidth / command overhead in regards to getting > the data out to the units. That's exactly right. In practice it worked out just fine. The only drives that got too far behind the leader to benefit from the system cache were drives with bad media, with which we had a lot of problems in the early days. At the time TDK made the only media the drives got along with, but it took a while to learn that. Linux, at the time, was supposed to support the UDF format, but every time I tried to format or copy onto the media linux would lock up tight and require a reboot. My biggest surprises were how bad most of the media were (or how poorly the firmware on the drives handled problems) and how much of the "10 MB/sec" of bandwidth wasn't really available for transferring data. I still can't thank Ken Merry enough for helping me through, tweaking drivers and everything. --- David To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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