Generic check for error ORA-15042

Error ORA-15042 means asm cannot mount the diskgroup as some of it member disks are not visible to asm.

How to find which disk is missing:

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- Scan the asm alert log for last successful mount of that diskgroup, where it will list out the disks with which it was mounted. Search for below keyword

SUCCESS: diskgroup <diskgroup name> was mounted

- After that point to till issue time scan in asm alert log that what are the disks added and dropped.

- Finally, make a list of disk path and name which were member of diskgroup before issue occurred.

Diagnosis:

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