Compressed backup

David Bolen db3l at
Thu May 23 13:07:23 EST 2002

Matthias Munnich [munnich at] writes:

> No! Only the sender side has to compress the data. The comparison
> could be done in the compressed data format. With the -z option 
> the sender compresses the data anyway. The checksum test should
> be faster for the smaller compressed pieces.

Except that you'll probably end up retransmitting the whole thing due
to the change in compressed output.  Since a compression function is
essentially a data randomizer (the better the compression the better
the randomization of the output), tiny changes in input can result in
huge changes in output.  That's the traditional problem of trying to
use an algorithm like rsync's with compressed file formats.

You really need to apply the rsync algorithm to the uncompressed files
if you hope to gain any real efficiencies in terms of reduction of
traffic transmitted.

-- David

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