Add option --time-only

[steinhh]

We maintain an archive with Solar observations (46 million and counting), with the files originating at another site (Japan). Naturally, we use rsync to fetch the files. Some observations are stored uncompressed at the origin, but we would like to store them compressed. To actually save space (i.e., to prevent having to store both compressed and uncompressed versions), I have created a tiny patch that adds an option called --time-only:

0. --time-only

   This modifies rsync's "quick check" algorithm for finding files that need
   to be transferred, changing it from the default of transferring files with
   either a changed size or a changed last-modified time to just looking for
   files that have a changed last-modified time, ignoring size changes. This
   is useful when remote files are uncompressed but a local copy should be
   stored compressed, togethe, with a zero-size stub to prevent re-transfers.
   This option is only useful when pulling files, as it requires post-transfer
   compression and truncation of files whilst preserving the original
   modification time of the stub. Thus the option is not transmitted to the
   remote side, also preventing the server from croaking on an unknown option.

I hope you will accept this extremely simple patch (only 3 code lines modified, two of which are declarations of the flag), which I have found very useful (saves me several terabytes of storage space!).

Sincerely,
Stein Haugan
Institute of Theoretical Astrophysics, University of Oslo

[pjotrek-b]

This sounds very useful!

I'm working with similar scenarios with synchronizing large scale archival media contents across sites.