I have been looking for ways to backup my photos on my phone. I own a drobo and recently installed Syncthing. Its wonderful! Now if you do not have a drobo and want something simple Sync.com is a nice TNO(trust-no-one) cloud service.
To start with Syncthing install syncthing on your drobo or PC. Syncthing for drobo can be found on this github:https://github.com/vrillusions/droboapp-syncthing and for normal computers check syncthing.net
Now on your android install Syncthing-Fork. This version has more options for conditions for when to sync and more battery saving settings.
Now from either device Add the other. I would recommend looking for the PC/Drobo via the phone so you can use the QR code. Leaving all the other settings alone for the device. You should not need them for this.
Now that the devices are connected lets great a folder to sync. From the phone find your photo storage. I am using /storage/emulated/0/DCIM/. Toggled your PC/Drobo on devices. Change the Folder Type to Send Only. Then I have my sync conditions set to when connected to wifi. Save this. Look at PC/drobo for incoming share and accept it and select where to save it. Save the folder settings on the PC/drobo.
*To keep the photos on PC/Drobo but to be able to delete them off your phone to keep free space. Look for this setting. From the main screen of Syncthing click Actions> Advanced. Look for “Folder ‘Camera’ (blahblahblah)” or whatever you named it. Click to expand options. Look for “Ignore Delete“. Check the box. Scroll to the bottom and hit save. Now you are all set!