Harry Putnam <[EMAIL PROTECTED]>:
> Using rsync (not concerned here with its shortcomings under rcp.el)
> one always gets a message about "speedup": Speedup is 167.27 or
> something similar. Interpreting this is not documented in rsyncs
> manpages. Only a general reference that rsync speeds up file
> transfer.
[EMAIL PROTECTED] (Kai Gro�johann):
Some things are still vague, though: rsync can use compression,
similar to gzip. Does the speedup figure take that into account? If
the source and target files differ in size, which size is used for
comparison?
That's easy: just do some quick experiments (which I append at the end).
The speedup is computed as (size of data that would be transferred by
rcp)/(sum of data sent and received by rsync).
The figures take compression into account, so the speedup is greater
with compression on. Notice that the forward and reverse data are
summed, probably because the way rsync works is non-duplex, so this is
reasonable.
================================================================
$ ls -l b
-rw-r--r-- 1 pot pot 3624 Jan 19 16:08 b
$ rm -f a; rsync -v b a
b
wrote 3696 bytes read 32 bytes 7456.00 bytes/sec
total size is 3624 speedup is 0.97
$ rm -f a; rsync -zv b a
b
wrote 1391 bytes read 32 bytes 2846.00 bytes/sec
total size is 3624 speedup is 2.55
$ rsync -v b a
b
wrote 92 bytes read 68 bytes 320.00 bytes/sec
total size is 3624 speedup is 22.65
$ rsync -zv b a
b
wrote 68 bytes read 68 bytes 272.00 bytes/sec
total size is 3624 speedup is 26.65
