Today, I realized that the mobile Internet while on the move has become fast enough to allow backing-up data residing on servers at home to an external hard drive connected to my notebook while traveling. This is a bit of a strange scenario, but let me explain:
Usually, the backup runs the other way around: Members of the household are on the move and their notebooks are automatically backed-up to a server at home whenever the backup script detects there is a suitable Wi-Fi nearby with a good uplink speed. But when I travel myself, I want to be sure I have a current backup of these devices with me, just in case home network connectivity fails. Yes, I know that’s perhaps a bit too much redundancy, as the likelihood of one of the notebooks failing and home network connectivity being lost at the same time is very, very small. But still.
Anyway, rsync is very efficient when synchronizing directory trees over the network. Instead of transferring complete files, it looks for differences in files and only transfers the delta. So if only a few megabytes in a 5 GB file change, only the few megabytes are transferred. This is usually the case in my scenario, so keeping a backup current over the Internet in which files with a total size of 10 GB change only takes around 200 MB in my case. No problem with today’s monthly data buckets. Obviously if a large video file suddenly shows up, that has to be fully transferred. But rsync has a nice ‘–dry-run‘ option, so an exception can be defined, should the monthly data allowance be too small.