Hello. Yes, you may use an old hard drive as a replacement drive. You will have to clear the Foreign Configuration when prompted, Do Not Import the configuration.
Hi All, is it possible to use old/used HDD to replace with faulty HDD in Poweredge R720 server for RAID 5?   Regards, Agha  
replacing faulty HDD with used HDD in Poweredge R720 for RAID 5