1) It is stored in all ASM Disks header and contain information
Disk group name,Physical size of all Disks in the Disk Group,Allocation Unit (AU) Size,Disk Own Size
,Failure Group,Name of Disk,Creation Date,Redundancy Type
2) Metadata is also stored as ASM file on ASM disks. These Files are internal to data and has file_number less than 256. This is the reason when creating Database on ASM have SYSTEM datafile as file_number as
256 and onwards.
ASM Files are Not listed in V$ASM_FILE (file#
File#4: Continuing Operation Directory (COD).
3) Metadata is always mirrored across three disk ( if Available) even you
are choosing EXTERNAL REDUNDACY.
4) Metadata is also stored in SGA of Database Instance copied by ASMB