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MiniDVs as a Backup Medium? 39

Posted by Cliff from the 15gb-for-$5USD-a-pop dept.
Matey-O asks: "Having purchased a MiniDV camcorder for the impending arrival of my twins (I suspect a majority of camcorder sales HAVE to be bought by new parents), I also purchased the firewire connection kit. Based on the software estimates on how much uncompressed video can be stored on the harddisk, it looks like a 60 minute MiniDV cassette holds about 15 Gb. Since the PC can control the camera, and the transfer is billed as lossless, has any work been done on using MiniDV as a backup medium? One Cassette looks like it'd store ALL of my important info, and at $5 per, it'd be pretty economical too." Reading this definition, it looks like the submitter may be mistaken about the 15GB size, and the Backfire pages at Sourceforge indicate a more realistic figure of 12GB. Backfire itself looks like it might be the project the Matey-O wants, but the last update is from April of 2000. Has anyone taken up this idea and tried this particular backup path, before? Is it a practical alternative to your standard computer tape drives?
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MiniDVs as a Backup Medium? More

MiniDVs as a Backup Medium?

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  • tape backup (Score:5, Interesting)

    by TheSHAD0W ( 258774 ) on Sunday November 24, 2002 @11:46AM (#4743170) Homepage
    Tape backups for PCs have been around for literally decades, and they've always been problematic. I'd really have to recommend against using a MiniDV backup solution, especially one where neither hardware nor tapes are meant for data back-up. The transfer may be "lossless", but the tape may not be; a drop out on the tape that would cause a slight blip on the video would ruin your data unless you used a sophisticated error correction scheme (which would also use up a lot of the data space), but even a great ECC might not avoid the many dips that might be present on a tape meant for video use.
    • Don't DVs use the same DAT tapes as DDS3/3 DAT drives?

    • Re:tape backup (Score:3, Informative)

      by Tom7 ( 102298 )
      I'm with you on this, but I don't see why you think error correction would take up a lot of the disk space. You usually don't need very much overhead (ie, more than the expected error rate on the tape) to get a good probability of being able to correct the data.
      • Because an error on the tape isn't a dropped bit; it's usually a big blotch of missing or irregular ferrite coating on the tape, and takes out a big block of bits. You need quite a bit of redundancy and good error-checking algorithms to fix this.

        Data-grade tapes are screened for this sort of thing, though even that screening isn't perfect; for video grade tapes, where that blotch would merely become a blip on the screen, quality control is a lot less strenuous, and you might find strings of such anomalies, which would probably ruin any chance of data recovery.

        On those VHS VCR tape backups, which were mentioned in another response, I believe the gizmo recorded triple-redundant data (each block written three times) in order to compensate for these sorts of problems. It didn't always work.
        • It doesn't really matter whether the errors happen in chunks or in the individual bits. It's easy to simply store redundant chunks (like RAID does) so that the data can be recovered even if a block fails. Using a code based on solutions to linear equations, for instance, you can have it so that you only need (say) 6 out of every 9 blocks in order to recover the data perfectly. These numbers can be adjusted arbitrarily, and as I said you only need about the same amount of redundancy as you expect your tape to have failures.

          Of course, if the errors really are on the tape from the start, then detecting bad areas of the tape and writing around them is even better!
          • There is allways the posibility of proofing the tapes first by writing out a test pattern and reading it back. Granted this takes time (a few hours by my math) but if somebody realy wants a low densirty tape drive that costs more that a DLT from ebay it would be doable.
    • The minicomputer at work (when I started. Mothballed a couple of years ago) backed up to a plain, consumer VCR for ages. Never had a problem with corrupt data. Never. Now, I am not dumb enough to assume that this is typical (given the technology, it's probably very atypical) but you are correct that it's been around for a long time.

      Personally, for stuff that you backup regularly, I'm recommending hard drive backups to friends and family. Get an extra drive on a removable tray when you buy new machine. One night per week, copy the whole mess over.

  • dvdbackup (Score:5, Informative)

    by hairy monster ( 22616 ) on Sunday November 24, 2002 @12:11PM (#4743304)
    http://dvbackup.sourceforge.net/

    • Re:dvdbackup (Score:3, Funny)

      by cryptor3 ( 572787 )
      From project description:
      We can not use all of the data, but 10 GB should be good enough for everyone.
      Obviously this guy is a quack. Everybody knows that 640 KB is good enough for everyone.

    • Re: dvdbackup (Score:3, Informative)

      by Omniscient Ferret ( 4208 )
      (checks page) Cool. There's an accompanying program that does error correction: rsbep [netic.de] takes up 14% with error-correction codes, but it can cope with 12240 consecutive bytes getting botched. So it can cope with (some) drop outs.
      • to be honest, as long as your new kid doesn't put a very small jam sandwich in the drive mechanism you should be ok.

        Just be careful with video editing software that supports batch capture. Media 100 (our professional video editing software) supports batch capture over firewire, and while it worked fine on the Pro hardware, the consumer equipment wasn't designed for control based on the timecode (not as accurately as the software was looking at anyway).

        It resulted in the camera shunting back and forth, mangling the tape, and it can't have done the camera any good either.

        Digitising a clip at a time worked fine though. Took forever though. I'm just glad that batch digitise worked well on our 184 minute DV-CAM tapes!

  • Err, 80-minute MiniDV tapes? (Score:3, Informative)

    by FeatureBug ( 158235 ) on Sunday November 24, 2002 @04:19PM (#4744800)

    The submitter is right, I think. The data capacity for a 60-minute MiniDV tape is about 12GB. However, for 80-minute tapes, the nominal maximum data storage capacity is 80/60 * 12 = 15GB per tape, which might reduce after FEC overhead to 12GB per tape.

  • You beat me to it... (Score:3, Informative)

    by blackcoot ( 124938 ) on Sunday November 24, 2002 @04:33PM (#4744893)
    http://dvbackup.sourceforge.net/ FWIW, http://www.schirmacher.de/cgi-bin/dclinks.cgi?acti on=view_category&category=Linux+Software [schirmacher.de] has whole bunch of DV software. While you're at it, you may want to check out Kino [schirmacher.de] which appears to work great. For more fun software to use with your DV cam, check out Arne Schirmacher's [schirmacher.de] pages. Good luck ;-)

  • In a word: No (Score:1, Insightful)

    by Anonymous Coward
    A bad idea, because DV recorders do not perform error-correction or "forward confidence" on data written to them. This is a really bad idea and I wish people would get the hint once and for all.
  • ...but this is like buying a car because you needed a cigarette lighter.

    - A.P.

  • What kind of crack are you smoking? (Score:3, Insightful)

    by Anonymous Coward on Sunday November 24, 2002 @07:24PM (#4746390)
    Is it a practical alternative to your standard computer tape drives?

    Short answer: NO .

    Longer answer: I'm a film student, I've been working with MiniDV a lot the past few semesters. MiniDV, especially with the cheap ($5!) tapes, is very prone to dropping frames; you lose a frame on a good shot and it's an annoyance, but translate that into data backup and it could mean losing a piece of a file. How much do you value the data you're backing up? If you're bothering to back it up, you probably value it more than that.

    MiniDV has its flaws as a video format, so much so that Sony and Panasonic have come out with their own formats based on it to correct some of these problems (DVCAM and DVCPRO respectively). And that's what it was designed to do, and it still can't do it well. It wasn't designed for data storage. Use something that is.

    You can do something the cheap way, or you can do it the right way. People who value their data choose the latter for obvious reasons.

    --- I'm not a real anonymous coward, I just play one on TV.

    • Who's smoking? Frame drop != data loss (Score:5, Interesting)

      by FeatureBug ( 158235 ) on Sunday November 24, 2002 @09:26PM (#4747399)

      A dropped frame is a visual symptom. It doesn't tell you how much data was lost. A dropped frame doesn't necessarily mean all of the data or even any of the data for that particular frame is actually unreadable on the tape. Dropped frames have many temporary causes like dust particles on the magnetic tape, faulty cables, cosmic rays or strong RF interference hitting the electronics, buggy software, drivers or slow CPU in the case of computer DV decoding, etc. Granted, it could be a patch of tape is really damaged, causing tens or even x hundreds of bits to be lost.

      Whatever the cause, a camcorder's builtin error correction can usually recover from small amounts of bad data. That's good enough for making videos but not for making backups. By using an additional layer of Reed-Solomon error correction as used in Rsbep DV Backup [netic.de] bad data up to 12240 consecutive bytes can be recovered, not counting any additional lower-level bad data the camcorder's internal FEC may have seen and corrected. The Rsbep guy found he could make up to 0.5mm diameter pinholes in the tape without losing data! I've seen professional data-grade backup tapes lose data after damage to a much smaller spot of 0.2mm diameter. I would say backups on MiniDV with RS error correction are feasible and cost-effective at 4USD/10GB. At 3.6Mbps, DV backups are also fast.

      IANAFS but I've used a lot of different MiniDV equipment and I've never had a problem like yours with dropped frames. Maybe your DV camcorder has dirty/misaligned/worn heads any of which could cause dropped frames.

    • Actually the difference between miniDV and DVCPRO has to do with the bitrate and encoding. The bitrate is double that of miniDV (50mbps vs 25mbps) as well, the sampling rate for DVCPRO is 4:2:2 as opposed to DV's 4:1:1 (or if you're using a PAL system, its 4:2:0 for standard DV). However the method of the digital delivery is identical between the formats, from encoding format to supported audio formats.

      A good backup solution would be a DDS Dat drive from my experience. Tapes are generally cheap (15-20 CDN for DDS-3 tapes, which offer 12GB uncompressed), and the tapes are certified for backup use and support proper error correction, as the DV format does not have great error correction for data (due to how the data is structured on the tape for video vs raw data). The downside however is that a DDS drive can be expensive for a newer DDS4 model.

  • To anyone using Firewire with Linux, which PCI card or motherboard would you recommend as the best most Linux-compatible solution to get Firewire ports?

    • Which is almost any PCI Firewire card out there.

      If it says, "VIA chipset", then it's almost guaranteed to be OHCI compliant.

      The only other 1394 host implementation I know about is the TI PCILynx chipset, and TI themselves have been moving towards OHCI. PCILynx chips are semi-supported under Linux.
      • Thanks for the info. Are there any cards that might fit the following description?

        I'd like to find a Linux-supported replacement for my current card which has all of the following on a single addon card:

        • analog video input with dual-standard PAL/NTSC,
        • analog video output with dual-standard PAL/NTSC,
        • 2 Firewire ports for digital video I/O.

        Unfortunately, Fast Electronics [fastmultimedia.com], the only maker I know of such multifunction single cards, only supports Windows and doesn't release programming info. I'd prefer not to use up 2-3 PCI slots by having multiple cards to do separately the tasks of video digitisation, video output and Firewire I/O.

        • Don't know of anything like that.

          If you go to Best Buy though, Dazzle sells an external analog video digitizer. (Analog to DV and I believe vice versa too.) Since it's DV it should work with any program that groks DV. (Kino, Cinelerra on Linux)
  • I'd love to be able to do this under MacOS X....any ideas anyone? Or am I stuck porting dvbackup?

    -psy
  • is that it's still tape. Tape still deteriorates over the years. You might want to convert it all to Video CD. You can get help to convert this lossless video to MPEG compressed video here. [dvdripguides.com]
    • MPEG-1, especially with VCD's frame size and bitrate, is EXTREMELY lossy. even mpeg-2, with dvd standards, is pretty lossy. but wasn't the point of this article backing up data? in which case, mpeg has nothing to do with it.

      and stop stealing my signatures man.

    • http://www.hydrogenaudio.org/index.php?act=ST&f=20 &t=4147

      I don't think anybody will ever have a CD-R last as long as a tape can without a hiccup, even in the best storage conditions, meaning no sunlight, relatively constant temperature, controlled humidity, etc.

      CD-R ~ 5 years before you will start getting some unreadable CDs out of a fair sized batch
      Tape ~ 20 years before the tape itself degrades to the point where you'll notice

      Now, a pressed video cd, on the other hand, would probably last a long time...
      • It depends on the grade of tape and the media used. Granted CD-R is more prone to failure, in the same respect, tape is as well. Most TV stations tend to back up their BetaCam tapes after 10 years, as that is the recommended shelf life before the tape starts showing noticable problems. Umatic 3/4 inch tape seems to last longer, although most footage has been backed up to BetaCam in some insitutions for simplicity.

        Time will always be an enemy when backing up data, as nothing lasts forever, so you always have to be one step ahead (and backup your data regularly before its too late).
      • CD-R ~ 5 years before you will start getting some unreadable CDs out of a fair sized batch
        Tape ~ 20 years before the tape itself degrades to the point where you'll notice

        I'm assuming that a tape that lasts 20 years before noticeable loss is much better than a low cost bulk tape. You should compare it to a similar CD-R.

        A high archival quality CD-R costs about $1.50/unit and has a shelf life of over two hundred (200) years. This is significantly longer than a production pressed CD is expected to live. Archival CD-Rs are the way to go.

  • deja vu (Score:2, Informative)

    by jayrtfm ( 148260 )
    Looks like nothing has changed since this was previously [slashdot.org] asked.
  • This makes infinitely more sense than an older, VCR based system i heard about years ago.

    Heck, with a really redundant error correction protocol, make it 6 gigs per tape, at $5 a tape, and "lots" of folks have these camcorders... it's a great idea!

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