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ORA-15075:

disk(s) are not visible cluster-wide
Cause: An ALTER DISKGROUP ADD DISK command specified a disk that could not be discovered by one or more nodes in a RAC cluster configuration.
Action: Determine which disks are causing the problem from the GV$OSM_DISK fixed view. Check operating system permissions for the device and the storage sub-system configuration on each node in a RAC cluster that cannot identify the disk.
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