Hello, can anybody help me, what should I do to resolve this alert :

DiskFolderClass 4 2         Disk Folder Production_512K requires 1 additional disks of class 10K to satisfy internal sparing requirements     Alert      Degraded            No          SpareHunger     Disk

This tier is almost free, no raid rebuilds needed, redundancy is dual, no alerts if it has insufficent disks to support parity raid, but.. Warning is active, I want to understand - why?...

thanks.