Configuring Hot Spare in AMI Megaraid Express 200 Raid Controller

Hi,
i have a Gateway server with AMI MegaRaid express 200 raid controller.The server has 4 , 9 GB hard disks configured as RAID 5. Recently the forth harddisk failed 3 times due to some problem in the controller. Every time I add a new hard disk , it works for 2-3 days and it fails.

I have the follwing questions.
Q1. Why it happens so?
Q2. How can I configure the fifth slot as a hot spare in case the forth slot fails again, Is it possible?
I tried this and the raid controller configures that slot and the harddisk in a different array.

Can someone help me..please.

Regards
V

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