I am an amateur photographer that also happen to be a Linux user. I do my back ups and sync’s using a linux application called rsync. I actually use the graphic front-end called grsync.
The command I use, including all the options is:
“rsync -r -n -t -v –progress –delete -c -s /source/folder /destination/folder”
One of the things I still need to test is the need for “-c”. That option, according the man page forces the skip to be based on checksum, not mod-time & size. In other words, the transfer of the file happens not only trigger by a change in the file mod-time or size but also any change in the checksum. That means that a checksum has to be created for every file in /source/folder and in /destination/folder and then compared. Including this option increases the sync time significantly.