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, second generation storage performance, maximum external scalability, and data protection for select HP ProLiant Gen8 rack servers 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 between HP Smart Array Controllers means customers can easily upgrade to future Smart Array Controllers. HP Smart Array Advanced Pack 2.0 firmware makes it easier for customers to protect their data with advanced functionality for this next generation of Smart Array controllers, including features such as RAID 1 ADM (Advanced Data Mirroring).