PowerEdge C6420 Supported Drives

Internal drive bay and hot-plug backplane:
Up to 24 x 2.5” HDD: SAS, SATA, Near-line SAS SSD: SAS, SATA 
Up to 12 x 3.5” HDD: SAS, SATA, Near-line SAS SSD: SAS, SATA 

Datasheet: C6420 spec sheet