Duplicati is free software and open source. You can use Duplicati for free even for commercial purposes. Source code is licensed under LGPL. Duplicati runs under Windows, Linux, MacOS. It requires .NET 4.5 or Mono.

Modifying the file system tab file is very dangerous. If you don’t know what you’re doing, or one letter is out of place, disaster can strike. That’s why it’s important to make a complete backup BEFORE doing anything within this guide. We also suggest uploading this backup to your Dropbox or Google Drive etc as a fail safe, in case you can’t access the file when you need it (for some reason).

If you have any experience with Rsync, you might know it's amazingly easy to copy your important files to a back-up location. As the simple example below shows, the logic doesn't really change much if you're using an external disk, a remote server running rsyncd, or running rsync over ssh:

Assign the new physical volume to an existing volume group (VG) or create a new volume group.

One issue with disk spanning is you have no control where the data goes. For example, lets say you have a 5MB powerpoint file. Half of that file may be in one drive, and the rest in the other. This will speedup saving and loading the file. On the other hand, if one of the SSD fails, your data is toast. This is true not only for one file but for all the data in the LVM partition as a whole. Say you create a single 750 GB partition spanning the 250 GB SSD and the 500 GB SSD using LVM. One of the SSDs fails. You will have half a partition. There is no way to recover any data from half a partition in the working SSD.