I experimented a little bit with the order of directories to backup in tarsnap.
Currently I use the following sorting algorithm:
- least frequently changed directory-trees first
Every change – even in meta-data – will affect the following data, as tarsnap is doing the de-duplication in fixed-width blocks (AFAIR 64k).
- for those directory-trees which change with the same frequency: list the bigger ones first
Implicitly I assume that the smaller ones are much smaller than the bigger ones so that the smaller part which will be backed up will not be noticed because of the bigger change. For my use cases of tarsnap this is true.
- if changes in a directory-tree are much much bigger than anything else, but the directory-tree has a medium change-frequency, put it even before less-frequently changing stuff
I do not want that a small change triggers a big backup, but a big backup can contain the remaining small part.
- if you backup home directories (even root’s one) and they do not contain much data, put them before directory-trees which change a lot daily
I do not want that a login triggers the transfer of data in other directory-trees which have not changed.