Hi Martijn - Thanks for the question. Yes, it is possible to do this. You need to use the "Validate data" operation. This can be used to perform one or more checks on the entire block data-set. If any of the the checks fail, you can stop the data from flowing downstream to the next block.

Connect your DataManager data flow to a Validate data operations block then switch to the "Custom" tab. Click the custom checkbox and then enter the validation formula:

RECORDCOUNT() >= [X]

where X is the minimum number of rows that should exist in the data.

Thank you Chris!