[Techtalk] creating smaller .iso files with tar ?

[Conor Daly]

On Mon, May 24, 2004 at 04:26:52PM -0500 or thereabouts, ed orphan wrote:
> I've been saving data from my crowed hard drive
> by burning CDs. 

>    My question is, could I squeeze more data onto
> a  700 Meg CD by using tar and gzip first, like:
> tar -cvzf  archive.tar.gz /my_data/is_kept_here/
>    And then creating the .iso, 
> mkisofs -r -J -o /archive.tar.gz  /data.iso  ?

It depends on how much data you have.  tar and gzip will squeeze your data
(unless it's all mp3 format) but you won't know, until it's done, how small
a particular archive will be.  You 'll end up doing multiple runs of 

tar czf archive.tar.gz /my_data/is_kept_here/selected_files
ls -sh archive.tar.gz

until archive.tar.gz is about 700Mb in size. Of course, you can use 'split'
to break a large tar.gz into 700Mb chunks but then you won't be able to read
files directly from CD, instead you'll have to reassemble the tar on HD and
then read out of it.

The other drawback to using a 700Mb tar.gz is what happens if the CD gets a
scratch?  Suddenly you lose all files beyond the scratch.  OTOH, if you have
multiple smaller archives (eg. 40Mb each) on the CD, you lose only those
files in the affected archive.

What I'm getting at here is the existence of 'mondoarchive'
(http://www.mondorescue.org) a GPL system backup and emergency recovery
tool.  It uses afio and bzip2 rather than tar and gzip and makes bootable
CDs with a fully interactive restoration tool on board.  It may be a bit of
overkill for your task but worth looking at nontheless.

Conor
-- 
Conor Daly,                   Please avoid sending me 
Met Eireann, Glasnevin Hill,  Word or PowerPoint attachments.
Dublin 9, Ireland             http://www.fsf.org/philosophy/no-word-attachments.html
Ph +3531 8064276 Fax +3531 8064247


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