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Some help with dd backing up into an iso




I am not very confident I am doing this right and it seems wrong,  I
can't locate any documentation that results into proper options.
I tried backing up an 8gb USB that has 2 partitions in it, one had 1.7gb
of data on it.
I used dd if=/dev/sdb of=usbfilename.iso
The resulting image was the full size of the disk.
To test the validity I restored reversing the order of the filenames
if/of  but that took for ever and it was a hog on resources.  After a
while I just gave up and killed the process.  I looked at the disk and
it seemed complete with all files in tact, so maybe I killed it
somewhere in the verification process.
So I used a program called etcher which I have used with 100% success in
the past and was surprisingly fast in burning images.
It took for ever as well, eventually it run a verification routine and
it was done.
Is there someway one can avoid creating such a large iso for no reason,
when the filesize is a fraction of the whole disk.  One way I thought of
was to shrink the partitions to just about 99% full, and leave the blank
part of the disk as not allocated.  Would that help?
Is there some fancy command line that does just that?

Thank you in advance




-- 
 "The most violent element in society is ignorance" rEG