Re: [rdiff-backup-users] Measuring transfer size

[Simon Hobson]

Thijs de Zoete wrote:

> I've measured the transfer size myself, and it came to notice that 
> the sizes sent over the connection are fairly small compared to 
> other backup tools with default setups.
> I guessed the files are being gzipped before they will be transfered.

No, I believe it uses the rsync protocol so only changed parts of 
files are transmitted. The protocol is clever enough to work out when 
bits have been inserted or deleted. For example, if you insert 1 byte 
at the beginning of a 1GB file, most tools would find every block of 
the file to have changed and copy a whole gig - rsync works out that 
the contents have moved along and only copies a few k.

rsync can also compress the data that is sent, but the key feature is 
eliminating so much data transmission in the first place.

Add in the facility (in the rsync tool) to limit bandwidth used to a 
specific value, and you get a very powerful tool for backups across a 
slow link - I've been using rsync for this for many years.


http://en.wikipedia.org/wiki/Rsync
http://rsync.samba.org/tech_report/tech_report.html

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Simon Hobson

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