Re: tramp (2.1.15); Unclear doc for rsync method

[Adrian Phillips]

>>>>> "Kai" == Kai Großjohann <address@hidden> writes:

    Kai> PS: I just assume, but haven't tested, that "rsync
    Kai> $REMOTE_FILE $NEW_LOCAL_FILE" runs at about the same speed as
    Kai> "rsync $REMOTE_FILE $RANDOM_LOCAL_FILE" for the same
    Kai> $REMOTE_FILE.  ($NEW_LOCAL_FILE is a file that does not
    Kai> exist, $RANDOM_LOCAL_FILE is an existing file with contents
    Kai> that are very different from the contents of the
    Kai> $REMOTE_FILE.  Perhaps if $RANDOM_LOCAL_FILE is very large
    Kai> then this does not hold?)

I wouldn't assume that - from what I understand when rsync copies to a
new file it is just an optimised scp but when a file already exists
then there is a lot more I/O, to read and build the checksums, from
the -W option :-

  The transfer may be faster if this option is used when the bandwidth
  between the source and destination machines is higher than the
  bandwidth to disk (especially when the "disk" is actually a
  networked filesystem).  This is the default when both the source and
  destination are specified as local paths.

I've used rsync extensively at work for tranferring large, quite often
"binary", files and whether one "wins" is very dependant upon
bandwidth, machine speed at other end, etc. Especially important for
checksum gains is that the new file is similar to the old.

Regards,

Adrian

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