2 May
2002
2 May
'02
10:06 a.m.
Re:
You would rather work the drive to death ?
You know, any really old tape you are attempting to recover
you really do not want to be running it thru the tape deck
very much
disks are huge these days, and the content is best messaged
on a new disk rather than an old tape.
Absolutely! Very good point.
However, if I notice recovered-reads (or hard errors) on old 9-track
tapes, I often see fewer recovered reads (or hard errors) if I try
the tape one more time. I assume that going over the heads once
may have knocked off a bit of dust/dirt/something that affected
the tape the first time. Note that I don't discard the
results of the first run until the second run finishes...
I've had one tape break during a second run :)
BTW, the only way you can be *SURE* you got all the data on
the tape is if *EVERY* read-request returned fewer characters
than you asked for. E.g., if you did:
bytesread = read(fromfd, buffer, BUFSIZE);
and you get BUFSIZE bytes in, then there's a chance that that
tape record had BUFSIZE + 100 bytes ... and you've just lost
those last 100 bytes.
Sure, sure ... it's not a major problem if you know the tape
format ahead of time. (E.g., MPE V tapes can't have records
more than 64 KB, and the actual limit is somewhat less than that.)
But the point applies to unknown tapes.
Stan Sieler sieler(a)allegro.com
www.allegro.com/sieler/wanted/index.html www.allegro.com/sieler
Unix will treat any device as a stream of bytes
And therein lies the problem. Go buy a
9-track drive and hang it on your *nix box.
Let me send you a 9-track tape. You read it any way
you want. You send me the tape back.
> Then you go get a second tape, and put the data back on
> any way you want. Then send it to me, and I'll tell you
> if your technique works or not.