Re: Setting volume size for dump

[Claus-Justus Heine <Heine@physik.rwth-aachen.de>]

> 3. In setting the volume size, how can I correctly bring the compression
> factor of using zftape into account?

This is difficult. Generally, there is no easy way to predict any
compressors efficiency unless one knows which kind of data is going to
be compressed.

When compressing ordinary files I would say that you'll get about 55%
of compression (i.e. the compressed size is 55% of the original size,
or around that).

When compressing data that already is stored in an efficient way --
sound data, compressed images (gif, jpeg ...), compressed files (*.gz,
*.Z) -- then you'll get little compression.

I fear the only way to find out about the compression factor is to try
it out, and then waste a bit of the tape capacity for safety. If you
measure an average compression factor of say 55% then I would suggest
to calculate with 60%. 

Cheers

Claus



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