[rescue] Slow DDS backups

Jeffrey Nonken jeff_work at nonken.net
Mon Apr 21 09:00:40 CDT 2003

On Mon, 21 Apr 2003 04:22:12 -0700, Jochen Kunz <jkunz at unixag-kl.fh-kl.de>

> On 2003.04.20 19:29 Jeffrey Nonken wrote:
> > > DATs are write wonly backups...
> >
> > Eh?
> >
> > How do you mean?
> Sotty, that was an old mail that escaped out of some normaly unused
> spool dir...
> I made the experience that you can write backups to DAT tapes without
> any trouble, but getting tha data back from the tape when you need them
> can be a nightmare. (Once I had to read three tapes to get a complete
> restore. Fortunately the data in question was static so I could use
> tapes from different backup generations.)

Ah. We have had different experiences, then.

I have had trouble with DATs, though. For the record, I've had the least
trouble with DDS-3. (I haven't used DDS-4, so I can't comment.) I've used
mostly -1 and -3, and I'm told that -2 are less reliable than either due to
the design.

At this time I have at home a complete, automated backup system based
entirely on DDS-3 tapes and a Sony SDT-9000 drive (plus more recently an HP
drive a friend gave me -- Hi Koyote!). I've mostly been using used tapes
that were obsoleted by my former employer (we upgraded to AIT-2). I've had
amazingly little trouble -- I think I've tossed maybe 3 tapes in >2 years.
Not bad, especially considering how much use they got before I got them.

I know that many people do backups for years and don't realize they're
screwed because they never test. Then they go to do a restore and it fails
utterly. So I will note particularly that, yes, I have done a number of
restores; both onesy-twosy files and complete systems. (I once restored my
laptop 3 times in a row, each time falling back a week, because I was
trying to get past a bad install that made the system flakey, and I had
tried to ride out.) So far, any time a tape has failed on me, it's been
caught in the backup process.

I've found DAT backups to be quite reliable if the drives are maintained.
The heads are pretty easy to burn out -- I smoked a set of heads in an HP
library before I found out they had a 12% duty cycle. (Which, I noted to
the customer service rep, was a fact not mentioned in the manual. They
replaced the drive with no further questions, and I changed my scheduling.)
(I note also that the Sony drives have a 20% duty cycle, or so I've been
told.) Most of the problems I've had were from ageing drives or worn tapes.

I also clean the heads regularly, after approximately 10 hours of use. I
use a recommended head cleaning tape, and replace it when it's used up.

Anyway, I don't doubt that DAT has had its problems, and you're not the
only person who's had problems with it. But I also wanted to show that they
can work well. Just leaping to the defense of one of my favorite tape
formats. :)

The truth is more important than the facts.

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