Adding drives with data on them

Hi Everyone,
I am new to this can anyone answer this question for me, I have two lenovo units with drives in them, I have just purchased the Drobo N5 with two 4TB drives. I have set these up and all seems good, my question is if I were to plug in my drives from my Lenovo units would all the data be lost or would it see that there was data on them or do I copy the data across first and then put them in the Drobo unit.
Many thanks

When you insert a drive to Drobo, it will automatically erase the drive and format it. I recommend you copy your data someplace safe, then copy it back into the Drobo after drives have been added.

From the Getting Started Guideā€¦
Warning! Any pre-existing data on the drives will be erased when inserted into the Drobo 5N