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From: uhclem@nemesis.lonestar.org Date: 23 Jul 94 13:41 CDT Newsgroups: comp.os.386bsd.questions Subject: Re: SCSI CDROM: "soft error (corrected)" ? Message-ID: <12@nemesis> Path: sserve!newshost.anu.edu.au!munnari.oz.au!bunyip.cc.uq.oz.au!harbinger.cc.monash.edu.au!msuinfo!agate!howland.reston.ans.net!cs.utexas.edu!convex!seas.smu.edu!rwsys!nemesis!nemesis!uhclem Lines: 50 <> [0]The CDROM is otherwise fine. Is this a problem with the media, the drive [0]or the driver? The media is brand new and has no visible defects. The drive [0]is a SUN SCSI drive. The controller is an Adaptec 1542B. The Red Book standard (the standard for audio discs, but is the basis for other formats) allows a "good" disc to have quite a number of BLERs (errors) per second when manufactured. The error basic error correction for audio discs can handle individual errors as large as 1440 bits in a row that are unreadable. (Sony claimed at one point that this is the diameter of a 4mm hole drilled through the disc - DON'T TRY THIS AT HOME!) 2048 byte data sector discs have additional ECC to handle larger errors and provide layered protection. The bulk of the error correction on CDs is there to allow the manufacturing process to be less-than-perfect, not to allow the customer to scratch the discs or leave them on the dash of the car during the summer. Since the introduction of CDs, the manufacturing process has gotten better, but ALL discs have correctable errors when they leave the factory. A disc stored in total darkness and never used will "grow" errors over time. How quickly depends on temperature, humidity and materials used during manufacturing. (3M warrants their data discs for 25 years now against uncorrectable errors.) Unlike hard disks and floppies, CD drives will use the ECC to fix data errors before resorting to something like trying to re-read the frame on the next revolution. All the ECC data needed to fix a major error is available within 8 more frame-times, which is sooner than a full revolution. (Exception: Some Mitsumi drives don't have enough RAM to do the ECC in the drive and its up to the host driver to do ECC corrections. Not all Mitsumi drivers do this.) Most drives are able to report when they invoked error correction and which level of correction they were forced to use. Most drivers don't report this bit of trivia unless the data can't be recovered at all. Sounds like your problem is an overly-chatty driver. I have a similar complaint about the FreeBSD floppy driver. Stick in a write-protected floppy sometime and try to write to it and see what comes out. Whatever ever happened to a short and simple "Drive %d is write protected"? :-( Frank Durda IV <uhclem@nemesis.lonestar.org>|"How do I know? A few dozen or uhclem%nemesis@trsvax.ast.com (Internet)| mastered CD-ROMs and a year ...letni!rwsys!nemesis!uhclem | or more of agony fixing ...decvax!trsvax.fw.ast.com!nemesis!uhclem | drivers for Mitsumi drives."