How long should you keep your backups?

I wrote this with tar. Which stands for tape archiver. It's 1600 BPI. That's bytes per inch.

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21 Responses:

  1. Lloyd says:

    Bytes per inch is an unclear metric, as it is clearly not part of the metric system, not decimalized, and not an ISO standard.

    You should be using octets per millimetre.

  2. Ryan Finnie says:

    My oldest backup is from 1998, a CD-R backup of a 320MB hard drive and part of a 510MB hard drive. Back when the media was $20 apiece, and the burner was if-you-have-to-ask. It only lasted about 15 years before starting to develop read errors, so no, CD-R is not an effective archival strategy.

    But its underside is gold, so there's that.

    • J. Peterson says:

      Realizing my access to 9-track drives was likely to go way soon, I remember buying my first CD-R in the early '90s. I paid nearly $100 for it (yes - quantity one), but as CDs go it was really pretty - gold on one side and emerald green on the other.
      Still worked when I archived it last summer.

  3. I have some of these but I suspect they are too fragile to read.

    • jwz says:

      Yeah, I only hung onto it because it looks cool. The tape appears to be in good shape, though.

      • irons says:

        Your regular readers know you were really looking for a viable aaa-60 termcap entry.

        • jwz says:

          You know, I hadn't read that post in a while.

          I really like that post.

          • k3ninho says:

            >It is also a great tragedy that you don't get DSR/DTR lines on these "modern" serial ports, which means you have to use inline XON/XOFF flow control. Like an animal.
            From a stable of great snark and honed prose, this is one of my favourite bits. Thank you.


      • Liam says:

        The issue will probably be with bleed-through. The magnetic bits on the film can affect the magnetic bits on the adjacent film when sitting like that for an extended period. Back when I worked in a Sperry mainframe shop with a lot tape and a legislative requirement that data be readable the tapes would be read and re-written to a new/different tape once a year to avoid the issue. So I expect that you would have to have the tape in storage for longer than a year to be at risk. It's low density, so it's not a given that you will end up as unreadable - just the longer in storage the more susceptible your data is to corruption.

  4. Bob says:

    I think I have some 9mm DAT tape backups from my Sparc from the early 90's somewhere around the house. I think there may be a SCSI tape device someplace to go with them.

    I used to have a bunch of punched cards from some programming I did when I was "younger" and there were some mylar/punched paper tapes from the TTY days as well.

    I do NOT have any microfiche that I am aware of, so I have that going for me,

    • tfb says:

      I'm disturbed to say that I have paper tape, or rather a paper tape. It contains a program to simulate hot-air-balloon ascents which I some day intend to read. I sometimes lie to people that it was written on some invented Victorian mechanical computer because understanding hot-air balloons was, of course, important to them. We used to keep it wrapped around the head of a wooden chicken, until the rubber band holding it together perished and broke.

  5. Jeff Bell says:

    Oh you had mag tape. We used to keep paper tape in a cardboard box in the middle of the road, every morning up to the mill for fourpence a month, cold punchcard chad porridge for dinner. Kids these days.

  6. MattyJ says:

    If I come across a backup that just says 'backup' and a date, and I don't remember what's on it, it gets tossed. I figure I would have put a few extra words on there if I gave a crap what it was.

    But then again, I'm unemployed and am wondering where that resume from 10 f'in years ago is.

  7. tfb says:

    There is an interesting curve of backup retention.

    Initially, you should definitely keep them because they're, well, backups that you might need to restore.

    Then there comes a time where you should almost certainly not keep them because they're too old to be useful as backups.

    If they survive that they become, accidentally, archives: perhaps that tape sitting in some box has the only remaining copy of whatever-it-is. So don't erase it.

    At the point where nothing will read the tape any more, well, whatever was on it is effectively gone now, so throw it away.

    At some point after that, one or both of two things happen: people become willing and able to do seriously heroic things to read really old media which might have the last remaining copy of something on it and/or the media itself becomes rare enough that it's not a historical artifact worth preserving. The second thing can't happen unless enough copies of the media get thrown away in earlier phases of the process: I don't think minidiscs would be interesting historical artifacts (yet), but if I still had a Fuji Eagle I would definitely not throw it away.

    Later still it becomes possible to print, cheaply, replicas accurate to the molecular level of the thing, at which point its value should drop to the cost of making another clone, but in fact people start spending huge amounts of effort authenticating the original copy of the object which is held to be somehow ineffably different to all the perfect clones. No-one, of course, actually knows which is the original: the people who have paid to have their copy authenticated as the original spend much of their time arranging to have the other people who have done that assassinated. I forget which film this is.

    • margaret says:

      i have a box in the garage w/ cassettes and diskettes and on those cassettes and diskettes are miner 2049er, oregon trail, flight simulator, et. al.. at this point its only because i hope to one day show the grandkids how old i am by firing up the apple ii and hearing it go "clunk clunk" again and bask in the glow of the green phosphor. but the virtual clones already exist online.

      • jwz says:

        It's probably too late for that, especially since "the garage" suggests high temperatures and varying humidity. My understanding (and experience) with VHS and audio tapes is that if you wind them through once a year or so, they'll last basically forever, but if left un-played they are destroyed by stiction, stretching and bleed-through.

        The good news is, if you didn't have anything particularly exotic or personal on those, Internet Archive probably already has an in-browser emulation of it all.

      • Jon says:

        That reminds me, I still have my VIC-20 in the basement. It's probably been a decade or so since I last tried to hook it up to my TV. It's going to be a bit more challenging now that I no longer have any devices with an analog TV tuner. I probably should have hung on to a old VCR just for that, but I got rid of my last one a few years ago.

  8. Nick Lamb says:

    If they have PII in them (and that's much more common than you'd think), no longer than the data subjects would have understood the data would be needed for its stated purpose when it was created.

    Of course in reality individual people are much worse than businesses when it comes to this, as you've experienced. Fortunately for them it's easier to pretend it's somebody else's fault you've got data you were supposed to destroy for one more friend-of-a-friend than for a giant corporation. And you'll buy it. "Yup," you say to yourself, "What I know is people have great memories, and they never lie, must be a giant corporation's fault somehow".

    But then this is a lesson you keep not learning right - it's like an attitude problem or something.

    Are these backups at least encrypt... ahahaha, I can't even stop laughing. Piles of tapes full of data that's not supposed to exist any more, it's like the stupidest S3 bucket stories except playing out in slow motion at ageing IT people's garage sales.

    One of the less obvious reasons to use decent symmetric encryption for backups: Instead of painstakingly erasing an old backup or needing to physically destroy the media (which would seem like a sin for some beautiful old storage) you can just forget the keys. 5TB of AES 256 encrypted data might proprietary source code or drafts of the next Great American Novel or just clown porn - but nobody will ever know without the key.

  9. Nrmrvrk says:

    Working my first computer job in the military, we had 4 late model IBM 3420 tape drives connected to our IBM System 370 mainframe. I worked nights so I got to run the weekly backups. After starting the backup job from the terminal, I'd walk back to the tape library and put my arm through as many mag tapes hanging on the "blanks" rack as I could. This seemed to be the easiest way to carry magnetic tapes without worrying about dropping them as you walked back to the tape drives.

    Luckily the tape drives were auto-loading so we didn't have to thread the tape through the heads and vacuum chambers and up to the second reel. I was always impressed that someone figured out how to make drives load/thread themselves. Huge time saver.

    It took about 40 tapes for the full backup and once you kicked off the job you just sat and waited for the sound of the vacuum release of one of the tape drive glass windows opening. This signaled that the tape was full and needed to be replaced with a fresh blank.

    Remove the full tape, put a new one on, and enter the new tape's number at the prompt on the system terminal. (Repeat for 3 hours) In the year I worked there I only ever remember one time having a problem with a tape. The leader sticker on one tape wouldn't register with the tape drive. I Tried the tape in two of the other drives with no luck then put it in the "to be fixed" box in the library for the day shift to worry about.

    I appreciated that we got to use magnetic tapes with our mainframe as the Korean Air Force folks we shared the data center with still had to use paper tape from time to time. (this was 1992)

  10. cthulhu says:

    I loved the tape drive I used back in the mid ‘80s on our VAX 11-780. You didn’t have to thread it; you mounted the tape on the supply hub, then it used a vacuum device to suck the leader onto the take up reel and to maintain the tension over the heads. Then a couple of years later we got a Convex mini-supercomputer, and you had to manually thread the tape onto the take up an animal. Oh well, at least it ran a flavor of BSD instead of VMS...

  11. Leonardo Herrera says:

    Well, this is my oldest backup.

    I think I know what's in it (code for a Windows CircleMUD area editor) but I don't know how in earth would I get it if I needed.

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