From OpenSCADAWiki
In Debian distribution case a separated partition for the working data storing, with the label "persistence", you need to create especial at anytime, and also into the file "persistence.conf" of the partition you need set the file system or it's part for reflection to writing (for example, "/home"). For reflection to all the file system into the file you need write "/ union". For the partition's file system better use "EXT3", and for it creation you can use a partition management program, for example "gparted".