SCSI Persistent Reservation (SCSI-PR) command support in disk firmware is a Microsoft failover clustering requirement. If Storage Spaces technology is being deployed in Windows failover cluster configuration then all the disk drives must implement SCSI-PR. SCSI-PR compliant firmware is available at http://support.dell.com for many disk drives shipped in the past. 

See the following table for the list of Dell HDD/SSD part numbers and the minimum firmware levels that have SCSI Persistent Reservation (SCSI-PR) support.

PR Drive Support 2_5_2014.xlsx