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Old 07-16-2003, 05:20 AM   #1
dtgarry
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Registered: Jul 2003
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backup on tape with MultiVolume


Hi to all;

I would like to backup my files on a tape, with the Multi-Volume option;

I am using Red Hat 9, and my tape is a dds-2, and on the tape is written that can handle up to 8GB for tape;

to backup I have used this command:

tar -cvf /dev/st0 - T listfiles --same-order -M -F script_change_volume -L 8388608

on script_change_volume I eject the tape, ask for an input, and exit;

after written the first tape, I have stop the tar, and verified the content of the first tape; its content size is 1.4GB only;

why?

someone can say me how to manage correctly the tape?

Thank you very much.
 
Old 07-20-2003, 06:16 AM   #2
icebird
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hi

nearly any tape drive i know cames with the ability to compress (hardware compression) the data written to it. so all the lableing (on tapes as well as on the drive) was done using the 'compressed' capacity. this capacity can only be reached with so called 'ideal' data (data that can be compressed at a level of 2:1 inputsize : outputsize). but this kind of data will only happen in test environments not in real live, even more the fact is if you try to compress already compressed data like zips or tiff/tga pictures etc. then the outcomming data you get is even bigger then the original one. as far as i know the capacity (with/without compression) of 4mm dat drives ar as follows:

dds = 2/4gb
dds2=4/8gb
dds3=12/24gb
dds4=20/40gb

normally you can tell the drive to not copmpress the data with a little switch on the pcb of the drive or by command of your backup software. i have switched off hardware compression on all my tape drives. if i get data that can be compressed i use the software compression of the tapesoftware wich is slower than the hardware compression. also there is tapesoftware that can switch on the hardwarecompression of the drive (veritas backup exec for example).

hope that answers your question.
 
Old 07-23-2003, 04:32 AM   #3
dtgarry
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Registered: Jul 2003
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OK, very thank.

After your answer, I have made other test, and I have discovered that if a tar directly a directory on a tape, the space occuped on the tape is greater than if I tar the same directory first on a my temporary tar, and after tar it on the tape.

Thank you again.
 
  


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