Oracle Error Message
ORA-15130: diskgroup “string” is being dismounted
Reason for the Error
The diskgroup is being dismounted by request or because an I/O error was encountered that could not be handled by taking the disks offline. A disk cannot be offlined whenever doing so could result in all copies of a redundant extent being unavailable.
Solution
Repair the hardware problem and re-mount the diskgroup. Refer to the alert log to determine which disks have failed.