Ask Slashdot: Keeping Digital Media After Imaging?

New submitter rogue_archivist writes "I'm an archivist at a mid-sized university archives, trying to develop a policy for archiving computer files ('born-digital records' in archival parlance). Currently old floppy disks, CDs, and the occasional hard drive are added to our network storage. Then the physical media is separated from archival paper documents and placed into storage. My question for all you slashdotters out there is: should these disks be imaged and then the physical copies discarded? Is there any benefit for keeping around physical copies of storage media long since rendered obsolete?"

Comments

The Medium Can Hold Secrets

[TechyImmigrant]

If you had a 1979 copy of Wizardry on an Apple ][ floppy disk, you could images the contents. But if you wrote them back to a disk and tried to run it, it would fail.

This is because as a means of copy protection, Wizardry used track arcing. Part of a track was written on a track. Another partial track was written half a head-step away. The timing of the writes was synchronized so the partial tracks didn't overwrite. Anyone doing a naive read and write, or even a not-so-naive scan of the half tracks would fail, because they would get the timing of the writes necessary to prevent collision and to meet the consistency checks in the program.

Obviously people reverse engineered this and wrote adaptive copy programs that you could direct to do the right thing, but how is an archivist going to know that?

If you can get this level of deviousness on a primitive floppy disk, I imagine that there is plenty of deviousness to go around on other formats.

Keep the media.

Re:DVDs only live for 7 years

[Miamicanes]

> I have burned CDs from 1995 that still work perfectly fine.

If they're redbook audio CDs, and your definition of "work perfectly fine" is "I can stick the disk in, hit play, it spins up at 1X, music comes out, and the player doesn't totally gag", you might be right. Now try ripping the disc using software that can monitor the realtime bit error rate. You'll probably be *horrified* to see how high it is.

Redbook audio CDs are very robust, even when their bits are rotting all over the place. They were designed in an era when hardware couldn't do much in realtime, so they bent over backwards to make sure they had a "plan B" to make sure the show would go on after the disc got scratched, dirty, or whatever else happened to it. They were designed so the audio data is interleaved in a way that when a read error occurs, the left and right channels get merged for 1 sample. A redbook audio CD has to be nearly *destroyed* (cracked, melted, fried, whatever) before it literally won't play, as long as the player is able to find the lead-in and sync up to the spiral track.

It'll start to sound "rough" and lose channel separation, but things have to be pretty bad before it will LITERALLY stop playing. At least, as long as the player itself is faithfully following the original redbook audio specs, and isn't trying to realtime-rip the audio to a ram buffer and play it back from there (which is what some, if not most, new optical-disc media players do TODAY). I have plenty of CDs that new players choke on and refuse to even try playing, but yet my 25 year old antique CD player that cost something outrageous like $600 or $800 when new, can play just fine. Apparently, it's because first-generation CD players were precision hardware that could blindly track a CD spiral as long as the disc itself was 100% within spec, whereas new players depend upon realtime error-analysis to stumble and wobble around, and make up for the fact that discs no longer spin precisely, and worm-gear optical assemblies no longer track with precision measured in microns.

That said, my experience has ALSO been that CD-R discs manufactured in THIS century are less likely to rot and become unplayable in new drives, but are more likely to have major problems with old players. The old players were precision hardware, and assumed the discs themselves were manufactured to precision specs. The first-gen CD-R media had dye that deteriorated over time, but their spiral tracks were spot-on, just like pressed discs. As drives got better at handling sloppy tracking, the discs themselves became sloppier.

Net effect: first-gen redbook audio CD-R media is likely to play with acceptable audio quality on an old CD player from the 80s or early 90s, but be unplayable on many modern drives & be un-rippable on most drives (some will allow you to spin down to 1X & emulate the playback mode of a legacy player if you're running a sophisticated ripping app). Newer discs that are still old will probably skip and have problems playing on an old player, but might still be equally bad on a new one. When today's bargain-bin CD-R media is 10 years old, it will probably be unplayable on anything, the same way my old VHS tapes from the 80s still play fine, but VHS tapes recorded after ~1998 are largely unplayable on anything I can find.

TLDR point: the storage life of "last-gen" CD-R media is likely to be better than first-gen CD-R media was at the same age, but enormously WORSE than that of the best "turn of the century" CD-R media (the golden era when quality standards were still high, and the worst faults of the first-gen media were addressed. Any box of CD-R media you buy TODAY is probably shit of the worst kind. The best media you can buy TODAY for long storage life? Non-LTH BD-R single-layer discs. But MAKE SURE they aren't LTH... most manufacturers don't go out of their way to scream, "These discs are LTH garbage!"

Re:Is there any benefit?

[cusco]

Just to reply to myself . . .

Target headquarters in Minneapolis gets VCR tapes from security systems all over the country, and they work with the FBI to read them and export the video. Security equipment manufacturers are notorious for using proprietary equipment or file formats to limit interoperability with the competition's systems, and they apparently have a lab that specializes in decoding them to extract the usable data.