Oracle internals, debugging and undocumented features
I just summarized few notes that I have used for troubleshooting ASM.
Placeholder for AMDU binaries and using with ASM 10g [ID 553639.1]
ASMIOSTAT Script to collect iostats for ASM disks [ID 437996.1]
Information to gather when diagnosing ASM space issues [ID 351117.1]
and of course you can always dump ASM block using
SQL> alter system dump datafile ‘<+DiskGroupName>/<Filename>’ block X; command to see it inside.