[H-GEN] Tape Drives

[Robert Brockway]

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On Mon, 7 Jan 2002, Michael Anthon wrote:

> The other method I have used is to use something like 'tar c stuff | gzip -9
> | dd of=/dev/tape'.  It's a little heavy on the CPU usage, but in the middle

The problem with gzipping just before you hit tape is that the effects of
an error in the gzip file (due to bad tape media) are more serious than if
it only a single file in a tape archive.

One suggestion is to gzip each file individually before pushing it to
tape.

> of the night, who cares?  The main reason I did this instead of using the
> drive compression was that the version of tar on the system in question had

I've found drive compression isn't all it is cracked up to be either.

> problems handling a few largish files.

> [2] As an aside, does anyone have any clue as to how to determine the
> remaining capacity on a tape?  It's something that's bugged me for a while
> and I can't find an answer to it.

Dump small files of known size to the tape & count how many you can drop.
Error is +/- half of the size of the file size.  You can count back to the
end of the "real" data because you know how many filesystem markers you
need to go back.  Ugly, you bet it is.  I don't recomended it except to
get an occassional idea of how much free space is at the end of last
nights backup.
Rob

-- Robert Brockway B.Sc. email: robert at timetraveller.org  ICQ: 104781119
   Linux counter project ID #16440 (http://counter.li.org)
   blake: up 43 days,  2:27, 12 users,  load average: 1.00, 1.00, 1.00
   "The earth is but one country and mankind its citizens" -Baha'u'llah


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