Dell Poweredge servers have a hardware RAID controller, with RAID control panel. When you boot the computer, it asks if you want to enter the RAID control panel by pressing CTRL+S. Once in the RAID control panel, you can check which HDD has failed. And check what type of RAID you have (eg) RAID 0, RAID 1 etc. If it is a RAID 0 (striped set across two or more drives) then all data is lost, you can replace the failed drive, but you will have to reinstall. If it is a RAID 1 (Mirrored drives) Or RAID 5, RAID 10 then you can replace the Failed HDD, and boot back into the Dell RAID control panel and choose to Rebuild the array. This should restore the data. This is not a way to avoid backing up, which you should also do in case of failure.