Runevn,   Despite it being called a SAS backplane, it does support SATA. Would you clarify the backplane part number you have installed? As seen below these are the backplane options for the R620.     Let me know if this helps.  
Hi,  I have a R620 with a SAS backplane and I want to change this with a SAS/SATA backplane. But I have trouble finding the right part number. Furthermore, I would like to know if I can use the same cables on my SAS backplane for the SAS/SATA one? Any help is highly appreciated. Thanks
Dell r620 SAS/SATA backplane part number?