Drobo nearly full vs. Time Machine delete oldest

**I’m running Mojave 10.14.6 on an iMac 3.3 GHz Intel Core i7. I’ve a Drobo 5D. For the first time, I’ve a RED light drive and Drobo Dash is freaking out that space is about to be full, and to add another larger drive.

Time Machine’s paradigm is to delete oldest files to provide more room. Will Drobo Dash lock up the RAID or will it allow Time Machine to do what it does best? I don’t wish to go over 4Gb drives and don’t have the time for this cr*p. Help**