Can rsync compare/copy based on mod date and filename alone, ignoring file size?
Context: I'm trying to implement a two-stage backup using rsync. The first stage is onsite, and I have a bash rsync script to copy files from the source path to on-site storage, and this runs hourly. The second stage runs at night and uses rsync to transfer everything new/modified to an off-site data center from the on-site storage. Problem is, the on-site storage boxes are filling up. Neither reducing the data backed up, nor increasing the storage capacity, is an option.
I've written a purge script to remove files a year old or greater every night on the on-site storage boxes, and replace them with empty touch files, preserving the timestamp of the original files-- this is to prevent rsync from copying the same file back from the source after the destination file is removed. But I can't figure out how to tell rsync to ignore file sizes; I need it to ignore compare/copy based on mod date and file name alone.
I've been through the man pages and have searched, and it doesn't look like this is possible. Is this correct? Any workaround ideas?