Force the 15K drive offline, remove it, insert replacement. If the 10K drive doesn't rebuild automatically, assign it as a hotspare. If the drive is showing "foreign", you must first CLEAR the foreign configuration before you can assign it as a hotspare. Removing and inserting the drive should be done HOT (while the system is running)!
Hello, I have a RAID 5 with three 10k drives and one 15k. I would like to replace the 15k drive with an extra 10k drive, so that I can use the 15k drive on a different server. What's the best way to do that? Thanks,  Ken
Replacing a PERC 5i drive in RAID 5