what you need

• some way to transfer your files from your mobile devices to your pc (e.g. a usb-c to usb cable)
• an external hard drive (or usb drive) with enough free space for all of your files
• the free software treesize free
• the free software freefilesync

preparation

• transfer all the files/photos/etc from your mobile devices into a folder called "phone backup" (or similar) on your pc
• clean up
  • organize and name everything
  • delete everything you don't need (and then empty your trash bin to clear up space on your device)
  • zip up folders that include lots (200+) of small files (many files, even if they are tiny, take long to backup)
  • zip up folders that include big files (like large video files)
  • tip: to find big files you can use treesize free. in this program sort first by size, then after checking all those folders, by file count
• get an external hard drive or other data storage (like usb drive) to copy your backup to. make sure it is big enough to hold all your data and more. if the hard drive has other things on it, create a folder "Backup".

the backup

• open freefilesync
• on the left column, select the folder(s) containing all your files on your pc
• on the right column, select the folder you want to put the backup into
• press "compare" to list all files and see which changes a backup would do
  • make sure there aren't any large files you don't need a backup of
• customize the filter to exclude folders you don't want to backup (for example movies, games, ...)
• press "compare" again to check your filter changes
• select the synchronisation mode "mirror" (or customize it however you need)
• run the synchronisation by pressing the button on the top right. this will take a long while for the first time, but each backup after the first one only copies new/changed files, and therefore will only take a few minutes.

after the backup, store your hard drive in a different house. this way a physical disaster (like a fire) doesn't destroy your device and your backup!