jw@sics.se (Johan Widen) (03/07/88)
[ This article was posted 21 Feb 88 06:53:16 GMT but was stopped on a machine ]
I was recently told that the rotating read/record heads in video tape players
are quite abrasive and that they tend to destroy the video tape in as little
as 10 passes. I was also told that the situation is even worse with DAT
(Digital Audio Tape).
Is this just the usual badmouthing of things new, or is there a real problem
here? I would like to hear from people who use VCR's for backup.
While we are on the subject: how many times should you be able to read
a reel tape? How many times should you be able to rewrite a reel tape?
--
Johan Widen
SICS, PO Box 1263, S-164 28 KISTA, SWEDEN
Tel: +46 8 752 15 32 Ttx: 812 61 54 SICS S Fax: +46 8 751 72 30
Internet: jw@sics.se or {mcvax,munnari,ukc,unido}!enea!sics.se!jwddl@beach.cis.ufl.edu (Don Lewis) (03/11/88)
As far as using VCR's to backup, I can't speak from personal experience, but I did work in the television industry for a number of years, and tapes were commonly used more than ten times. Often, though, after three or four passes (of recording, playback is pretty much irrelevant), the possibility of drop-out occurring was probably greater than 50%. Still, considering the cheap price of tape ($5 U.S. will get you a pretty decent tape), this is still not a bad deal. I'd be interested in hearing what everyone else has to say about this. As for the DAT's, I'm not sure what technology they're using to record and play with, so I don't know what the wear factor would be. -Don Lewis University of Florida Gainesville, Florida 32611 (904) 395-8812
paul@phoenix.Princeton.EDU (Paul Lansky) (03/12/88)
In article <JW.GNUS6@sics.se>, jw@sics.se (Johan Widen) writes: > [ This article was posted 21 Feb 88 06:53:16 GMT but was stopped on a machine ] > > I was recently told that the rotating read/record heads in video tape players > are quite abrasive and that they tend to destroy the video tape in as little > as 10 passes. I was also told that the situation is even worse with DAT > (Digital Audio Tape). I've worked with lots of different kinds of tapes over the years (I'm in computer music), lots of 1600BPI, 6250s, audio tapes, VHS and BETA formats for video and PCM, TK50s etc. The tapes I have had the most difficulty with have been BETA/PCM, using exactly the head technology that is used in DAT and the new 8MM VHS/2.3GIG storage systems. The PCM formats have massive error correction built in, but I have found that about 70% of the time if a tape is played more than 10 times or so, bad spots will start to develop because of the abrasiveness of the rotating heads. I don't know what kind of error correction the new backup systems use but given the density at which data is stored I think one bad spot will lose a LOT of information. But, once you realize that data is probably more fragile on these tapes the following precautions will probably make them as robust as other tape storage media. 1) Buy only the highest quality tape. For our PCM systems I use tape no longer than L500 in Beta. The longer tapes are thinner. I also recommend only using the highest quality. Sony-PRO tape is best. Given the cost of storage per Mbyte, even the MOST expensive tapes are a bargain. 2) If you have data that has to be archived and retrieved frequently from a given tape it is best to keep a master and work with copies of that master. We do this with PCM formats and it works quite well. I've stored many many gigabytes of signal files on 9-track tape over the past 15 years and only lost data once or twice, with careful use. I don't see how the new media can approach this level of reliability, particularly given the violent start/stop motion it is likely to undergo in various situations, but it is certainly worth a try. Paul Lansky Music Department Princeton University
soley@ontenv.UUCP (Norman S. Soley) (03/17/88)
In article <12685@uflorida.cis.ufl.EDU>, ddl@beach.cis.ufl.edu (Don Lewis) writes: > As far as using VCR's to backup, I can't speak from personal experience, > but I did work in the television industry for a number of years, and > tapes were commonly used more than ten times. Often, though, after three > or four passes (of recording, playback is pretty much irrelevant), the > possibility of drop-out occurring was probably greater than 50%. Still, > considering the cheap price of tape ($5 U.S. will get you a pretty decent > tape), this is still not a bad deal. I'd be interested in hearing what > everyone else has to say about this. What is that 50% figure based on? 50% of the tape has dropouts? or 50% of ten times recorded tapes have at least on dropout? The VCR backup schemes use multiple redundancy (the sales literature says 8 copies of everything) Sufficient to deal with case 2 but case 1 would wipe out your backup pretty thoroughly. I also have no experience with such machines I'm just respewing sales lit. -- Norman Soley - Data Communications Analyst - Ontario Ministry of the Environment UUCP: utzoo!lsuc!ncrcan!---\ VOICE: +1 416 323 2623 {utzoo,utgpu}!sickkids!ontenv!norm ENVOY: N.SOLEY {mnetor,utgpu}!ontmoh/
ddl@beach.cis.ufl.edu (Don Lewis) (03/19/88)
I didn't state my experience very well. When I referred to the dropout rate of 50%, I should have specified 50% of what. Well, what I meant was that after 3 or 4 recording passes, the possibility of any tape developing a "major" dropout (not counting the natural low quality at the beginning of the tape, and lasting for longer than 5 seconds) was about 50%. But, this is just a rough estimate, and (after keeping tedious logs for a year) we discovered that even among tapes from the same manufacturer and the same batch had different times before dropout occurred. What it comes down to is that you really can't place any high (or what I consider high) rate of reliability on the tape medium. And, you have to realize that even with everything being recorded "8 times", if a dropout lasts long enough, you'll lose that data. -Don Lewis University of Florida