To start i would verify that you have a complete backup of the data, if not then I would recommend looking into the option of taking the drives to a data recovery solution, as the following procedure has the chance of damaging or detroying the data if we are unsuccessful.
First thing to verify is if the controller is out of date. Let me know the version your Perc 6/i is at prior to proceeding, unless it is within a couple versions from current.
What we would need to try afterwards is to go to OpenManage Server administrator or to the Perc 6i BIOS and then FORCE ONLINE the OFFLINE drive. Once that is online then boot the server and see if the OS is accessible, if so then verify the data is intact. If it is then try rebuilding the failed drive afterwards. Now if the OFFLINE drive won't go online, try removing the drive listed as FAILED from the server and then see if the OFFLINE drive will go ONLINE.
Let me know what you see.