size database (db), backups (rdm)and restored database (db)

What database? SQLite? MySQL? MariaDB? MS SQL?

Regardless, databases and text files are very different. RDM manages then differently and offer different advantages, for example all of database based data sources support entry history, the .rdm format does not. These entries must be stored and take up more disk space. Databases will also contain schema objects like table structures, indexes, primary & foreign keys. Furthermore databases must manage things like physical pages of the disk and store transaction logs. So yes, a database will usually be (much) bigger than a simple text (XML) file. This is completely normal and to be expected. There are, however, ways, depending on the database used, to reduce (temporarily) this overhead disk space (compact the database). In most cases (most) experts will advise against compacting/shrinking of the database for a plethora of reasons. I will let you go down that rabbit hole on your own. You can also, in RDM, perform the cleanup actions for logs, entry history, and so on and so forth.

Best regards,

Hi Stéfane

I use SQLite.
Now it is explainable. The source db has things stored like entry history. When I do a automatic backup to a rdm
this information is not back-upt to the rdm I think. Therefor the rdm is 90% smaller. When I create a new SQLite database
and restore the rdm into it, it is bigger than the rdm because of the "Databases will also contain schema objects like table structures, indexes, primary & foreign keys",
but smaller than the source db because the entry history is still missing. Over time it will of course grow..

Yes, you got it, that is a good summary.

Best regards,