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Old 05-20-2004, 12:59 AM   #1
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Meaning of Compression level 'dump' command

Hi forum, I recently started to backup my entire system. I have a HP SureStore DAT24 and DDS-3 tapes to use with it. I use the webmin 1.4 filesystem backup interface to do the backup.

When I choose the compression level, I am not sure if the bigger I use the more compression I will get. The man of dump command doesn't clear this. Here is what I found (not a big deal, huh ;-)

-z compression level
    Compress every block to be written on the tape using zlib library. This option
will work only when dumping to a file or pipe or, when dumping to a tape drive,
if the tape drive is capable of writing variable length blocks. You will need at
least the 0.4b22 version of restore in order to extract compressed tapes. Tapes
written using compression will not be compatible with the BSD tape format. The
(optional) parameter specifies the compression level zlib will use. The default
compression level is 2. If the optional parameter is specified, there should be no
white space between the option letter and the parameter.
So assuming that 24,3 Gb of data couldn't fit on a tape with compression level 2, I will choose compression level 8 hoping that all my data will fit on that tape. Does anyone know the exact meaning of the compression level?

Thank you!
Old 12-30-2004, 03:34 PM   #2
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compression level means afaik what kind of compression is been used by dump:

Old 12-30-2004, 04:21 PM   #3
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Compression level refers to how compressed a file is. The higher number like -z2 would be more compressed than -z1 or -z0 but I haven't seen any mention of dump using -z8. Even if you could use -z8 , I think you would be waiting forever and a day to finish the job.
If dump is anything like partimage, the compression levels are accomplished by using different tools as chuettl said.
Old 12-31-2004, 09:05 PM   #4
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Don't use dump. It is obsolete and doesn't work with newer Linux kernels.


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