Data Computing Appliance V3
Data Computing Appliance V2
The Hot Spare drive appears as Spun Down due power saving feature , called "Dimmer Switch Feature" which might be enabled on some of customer’s Servers / RAID Controllers.
With Dimmer Switch, any unconfigured drive connected to a MegaRAID controller is spun down after 30 minutes of inactivity, reducing its power usage. Spun down drives are spun up automatically when you create a configuration using those drives, during Patrol Read and when needed in case of Disk failure in the same RAID group.
For a detailed step by step resolution please refer to EMC Support Solution 489505 https://support.emc.com/kb/489505