Date: Wed, 21 Jul 1999 12:03:33 +0930 From: Greg Lehey <grog@lemis.com> To: Mike Avery <mavery@mail.otherwhen.com> Cc: questions@FreeBSD.ORG Subject: Re: Recomended tapes form HP? Message-ID: <19990721120333.T84734@freebie.lemis.com> In-Reply-To: <199907141328.IAA25886@hostigos.otherwhen.com>; from Mike Avery on Wed, Jul 14, 1999 at 08:24:41AM -0500 References: <199907132304.SAA25026@hostigos.otherwhen.com>; <19990714160513.28515@mojave.lemis.com> <199907141328.IAA25886@hostigos.otherwhen.com>
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On Wednesday, 14 July 1999 at 8:24:41 -0500, Mike Avery wrote: > On 14 Jul 99, at 16:05, Greg Lehey wrote: >> On Tuesday, 13 July 1999 at 18:00:32 -0500, Mike Avery wrote: >>> On 14 Jul 99, at 1:16, Iani Brankov wrote: >> Now they *did* agree that DDS (which you call DAT) is evil. > > Well, there was some discussion there also. But whether they should > be called DAT or DDS seems to vary from vendor to vendor. DAT > is the physical form factor of the cartridge. Archive and Seagate > call their drives DAT drives. HP calls them DDSx, where X indicates > the level of the DDS format. Archive and Seagate tell you which > level DDS media to use. All in all.... I think picking on that point is > rather fruitless. The term is DDS. Agreed, the marketroids call it DAT, but what do you expect? Internally, the Archive/Seagate docco refers to DDS. And it may seem pedantic to you, but confusing terms can lead to trouble, and there's no necessity for it. >> They are some of the most unreliable drives on the market. I have >> yet to have one last two years, and I currently have replaced a >> drive with another of identical make, and I can't read my old >> backups. > > Odd. I have a 7 year old DAT (or DDS1) HP drive that's still going > fine. I did have lots of troubles with HP DDS2 drives (if memory > serves). After six months to a year, they needed to be overhauled. > If they were in warranty, HP did it for us. OK, what other computer equipment needs (expensive) overhauling every 6 months? > HP has played some games wherein they changed the compression > algorityms and made earlier tapes unreadable. A real problem for > people who need to recover data from older tapes. Do you have any details? I don't believe this is true, at least not for drives made in the last 5 years. > And Sony seems to use different formatting on it's DDS2 tapes than > other people, so it's a BAD idea to use Sony tapes with HP drives. They used to. They don't any more. > We'd be able to verify the backup and not recover data a week later. This sounds more like unreliability than compatibility if you ask me. If it had been a compatibility issue, the verify would have failed. > Worse, Sony tapes were easier to get than the other guys. Huh? > As a side note, a number of years back Scientific American ran an > article on the life expectancy of backups. Their conclusion was that > most backups were rendered useless by the march of technology > sooner than the media showed problems. I read that too. I didn't agree with it. It suggested, for example, that my 10-year-old QICs would no longer be readable. They are. > How much do you have on 8" floppy disks? A fair amount. > How much of it can you restore? None. I don't have a functional floppy drive. But a year or so ago I gave a copy of Seattle Computer Systems DOS/86 version 0.3 (also known as QDOS, the predecessor of MS-DOS) away to a guy in Canada. The floppy was about 16 years old and had been treated *very* badly. He had trouble reading it, but he got most of the data off. I'd expect much less trouble with the floppies I've been storing correctly. > Aside from that, they put the data life expectancy of DDS tapes at > 18 months to 2 years (if memory serves). Another case in point. I have data on DDS tapes that is 8 years old, and when I have a functional DDS drive, I can read it. > I was shocked, since we'd just converted from 8mm (which has a > somewhat longer life expectancy). In the end, I called 3M. Their > comment was that the report was correct, but incomplete. If you > store DDS tapes lying flat, their life expectancy is short. If you > stack them on edge, they are supposed to be good for 10 years. Interesting. Did they say why? > Of course, that leaves many people with the problem that the > current version of the backup software may not be able to read > tapes from the older version. (An area where *nix shines.... I hope. > Some commercial firms seem to have no qualms about changing > format and not making them backwards compatible.) Dennis Ritchie recently (early this year) dragged out some old 3rd edition tapes with the system source. To quote: The dates on the transcription are hard to interpret correctly; if my program that interprets the image are correct, the files were last touched on 22 Jan, 1973. The difficulty of interpretation owes both to possible bugs in understanding the date bytes on the tape, but also to epoch uncertainty. Earliest Unix used a 32-bit representation of time measured in 60ths of one second, which implies a period of just over 2 years if the number is taken as unsigned. In consequence, during 1969-73, the epoch was changed several times, usually by back-dating existing files on disk and tape and changing the origin. The OS here implements the present standard of a New Year 1970 epoch and a resolution of 1 second, but the DECtape on which it is stored uses the older interval and some older epoch. This doesn't sound like he had much trouble reading the tapes, which must have been 26 years old at the time. Greg -- When replying to this message, please copy the original recipients. For more information, see http://www.lemis.com/questions.html See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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