The HP Smart Array P421 Controller is a low profile, 6 Gb's, PCIe 3.0, Serial Attached SCSI (SAS) RAID controller that provides enterprise class, storage performance, maximum external scalability, and data protection for select HP ProLiant Gen8 rack and tower servers.

It features eight external SAS ports and delivers increased server uptime by providing advanced storage functionality, including online RAID level migration (between any RAID levels) with flash back write cache, global online spare, and pre-failure warning. Data Compatibility among all models of Smart Array controllers allows simple and easy migration at any time when needs for higher performance, capacity, and availability increase. Even new generations of Smart Array controllers can understand the data format of previous generations of Smart Array controllers.