VNX5400 has 4 x Vault Drive containing the OS which runs the whole storage system.

Here's few questions:-

1) Do we need to assign Hot Spare to the Vault Drive???
    But how to assign hot spare to them?  Do I need to form a RAID Group using those 4 x Vault Drive first?

   My worry is that since those 4 x Vault Drive contains OS running the whole system, should we assign Hot Spare to protect them?

2) Is it recommended to use the 4 x Vault Drive as Data Disk by forming a RAID 5/6/10 Group?

    OR is it better to keep the OS safe by NOT using those 4 x Vault Drive for Data Usage????

Please advise, thanks.