If you are using an encrypted or revision-proof database, you define the maximum size it can grow to when you create it. This is a hard limit, no different than the size of the internal disk on your Mac. Finite space can't hold infinite documents, so you need to be aware of how much space you have available. If you add more data than it can hold, you will receive errors in the Log window of popover.

If you run into this situation, please contact our support team.

Another thing to be aware of, there needs to be enough space available to do maintenance, like a database rebuild. To keep an eye on the space, periodically select it in DEVONthink, then choose File > Database Properties. At the bottom of the statistics you will see the space consumed and the available space to work with.