Re: rsync re-syncs unmodified files

[Rodolfo Medina <rodolfo.medina@gmail.com>]

Rodolfo Medina <rodolfo.medina@gmail.com> writes:

> When using rsync from pc to usb stick, it re-syncs unmodified files, which is
> annoying with large backups.
>
> In rsync man page, I found the following:
>
>    When  transferring  to  FAT  filesystems  rsync  may re-sync unmodified
>    files.  See the comments on the --modify-window option.
>
> And, the comment on the --modify-window option:
>
> --modify-window
>               When  comparing  two  timestamps, rsync treats the timestamps as
>               being equal if they differ by no  more  than  the  modify-window
>               value.   This  is  normally  0 (for an exact match), but you may
>               find it useful to set this to a larger value in some situations.
>               In  particular,  when  transferring to or from an MS Windows FAT
>               filesystem (which represents times with a 2-second  resolution),
>               --modify-window=1 is useful (allowing times to differ by up to 1


It is explained here:

    http://www.samba.org/rsync/FAQ.html

    Another common cause involves sending files to an Microsoft filesystem: if
    the file's modified time is an odd value but the receiving filesystem can
    only store even values, then rsync will re-transfer too many files. You can
    avoid this by specifying the --modify-window=1 option.

and confirmed here:

    http://ubuntuforums.org/showthread.php?t=886048

Apart from the fact that I can't understand how it's possible for a filesystem
to be unable to store odd numeric values!, the ls command with the --full-time
option shows to me that the timestamps are identical on both the source and the
destination: so, how can this odd-even difference be detected?

Contributes welcome
Rodolfo