Why can the hard drive I have used on my other devices not be formatted completely by the D2-310/D4-310/D5-300C/D5-300 ?

There may be several partitions on hard drives that have been used on other devices, and when creating a RAID to format the hard drive, the D2-310 may thus be unable to clear all the data on the hard drive at once. In such cases, a RAID must be created several times to ensure all data is cleared.