Hi, I am concerned about things I've read about CD-R longevity, and that the Orange Book specs apparently allow for a certain amount of errors - near as I can tell, this is taken into consideration when manufacturers give those 70-100 year archival life expectancies, that *some* errors are fine and dandy and that having just a few errors doesn't affect their lifespan ratings.
Well, errors might be okay for music tracks, but what about data? System software backups, app backups, and the like. Couldn't just *one* little misplaced "0" to "1" or whatever, spell disaster for whether or not an app or System folder backup would work right? I'm not talking about the immediate verification after burning a CD-R, as I always do that. I'm talking about the CD-R media or dye-layer gradual deterioration over time, even when stored away from light/heat/ moisture/other bad stuff. I have just decided that in order to verify the integrity of my CD-R data backups several years down the road, instead of just burning the whole partition in regular Mac format like I used to, I am now first dividing up the partition that I want to back up, into smaller folders (around 100 MB max), then making disk images (using Disk Copy, I have version 6.3) of each of those folders, with the "Verify Checksum" option enabled. Then I burn as many of those disk images as will fit, onto a CD-R. This appears to be a valid concept, at least to start with, as I can do a manual "compare" with Toast, after mounting the disk images that are now on the CD-R and verifying their checksums with Disk Copy, and the manual Toast "compare" thing shows that the disk-image version of the data is identical to the original. The idea of the checksum thing is that later, down the road, if a particular CD-R has some errors and one of its disk image's checksums won't verify or whatever, that I can probably find an error-free version of that file on one of my several other duplicate CD-R's of that exact same data - assuming that even if all disks eventually develop errors, that the errors would hopefully be in different locations on each CD-R, thus affecting different files - so by having duplicates, I ought to still be able to find a valid disk image file that will verify correctly. At least with the checksum, I would *know* there was an error, right? Whereas with just regular backups, there wouldn't be any way of telling if some file had gotten corrupted through media deterioration? (since I would no longer have the original partition that I burned the CD-R from, to compare it to) I've tested the verify-checksum thing with just the fresh CD-R's, and of course it works fine (they haven't had a chance to deteriorate/develop errors/whatever, yet). My question, however, is how reliable are those checksums? Does the checksum thing catch all errors or inconsistencies, or just some of them? Am I having a false sense of security by using the checksums? Hope you don't think I'm terribly paranoid about CD-R media, but... I've had 2 of them fail completely (right around the 3-year mark, even when stored correctly and seldom used, and even after doing the lens-cleaning thing and all that). Obviously in that case a checksum wouldn't do me any good, since the disk wouldn't mount at all. There seems to me to be a lot of things that the manufacturers don't bother to take into consideration when doing their longevity guestimations - which appear to be based mostly on extreme exposure to heat/light. I've been wondering about how other things affect CD-R, though, such as constant exposure to heavy corrosive coastal salt air (doesn't silver, like, corrode really easily? everything *else* around here rusts/corrodes like mad, even some stainless steel, which isn't supposed to happen) - and those thin plastic coatings on CD-R don't look all that impermeable, either (especially around the edges). I know, use gold media instead - however the 2 failures were both on gold media. You might wonder, why the fuss, why do I care, if backups deteriorate just buy new software or download more stuff. It will be a few years, after all, right, and it will all be outdated by then anyway? Well, not so fast there... here's the thing... Given my fixed income and no-more-credit-cards-anymore, it's quite likely that I'll still be using most of the exact same hardware 10 years from now (time goes fast, after all) - or at least from comparable vintage (1997-2001 or so). Maybe not for browsing which would need updated software, but most likely for my other expensive hobbies such as Photoshop, Painter, etc., which are fine the way they are and won't be getting any more updates, and the literally thousands of dollars worth of other legally- registered shareware and fonts and other software that it's taken me YEARS to accumulate - there's literally NO WAY I could replace all that software, starting over from square one. Hardware, that's easier to replace, and cheaper, and I expect that will be around for a few more years at least, but the software is what I need to make sure it's backed up securely. The last year or so, I've finally gotten all this just about exactly how I want it, and don't anticipate any further major changes, and I want it preserved with at least some sense of security that the data isn't going to get corrupted or have unacceptable errors in it. Or that at least I will know *where* the errors are, and can thus retrieve that specific file from another duplicate CD-R. I've just now switched from Kodak Gold CD-R (which apparently is no longer available; I finally used up the last of it that I'd bought previously) to TDK silver *and* Maxell "Pro" - making duplicate CD-R's on both the TDK and Maxell media. I don't really trust either brand of media, yet - a bit early to tell, y'know? Anyway I've been making several duplicate sets for each backup, some stored offsite just in case. And I always burn at 1X which I've read is better; my old Yamaha (CD-R, not CD-RW) only goes to 4X anyway, so timewise it's no big deal - I just go do something else while it's making the CD-R's. I'm just wondering, though, about checksum reliability, in general, and with regards to Disk Copy as well. Is Disk Copy's checksum as good as/the same as, other types? I'm sort of limited to whatever will run in my preferred OS, which is 7.5.5 (or 8.1 in a pinch, or for 'net, but 8.1 drives me bonkers for a number of reasons, even with Kaleidoscope and Mike Balonek's System 7 look-a-like scheme (the *best* IMO!! - thanks Mike) and some other goodies (all of which take the edge off, but I still have some complaints about 8.1 other than just its appearance, so I avoid 8.1 whenever possible). (If you reply, might have to "snip" most of what I said, so as to not bounce for over-size; right now it's 6K or so, but with headers and all might approach the 10K list limit) - Jamie Marie (re earlier unrelated question last week or whenever, am awaiting delivery of PRAM battery) . __________________________________________________ Do you Yahoo!? Yahoo! Web Hosting - Let the expert host your site http://webhosting.yahoo.com -- PCI-PowerMacs is sponsored by <http://lowendmac.com/> and... 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