From OpenSCADAWiki
In the case of Debian distributions, a separate section for storing work data, with the label "persistence", should always be created specially, and in the file "persistence.conf" on it also specify the file system or part of it to be reflected on the record (for example, "/home"). To reflect the entire root file system, you must write "/ union" in the file. As the file system of this partition, it is better to use "EXT4/3". To create a partition you can use the program partition manager, for example — gparted.