Last updated on July 17th, 2015 at 06:05 pm
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$ASM_FILE (file#
Details are available in X$KFFIL .In addition the first 2 AUs of each disk are marked as file#=0 in X$KFDAT
•File#0, AU=0: disk header (disk name, etc), Allocation Table (AT) and Free Space Table (FST)
•File#0, AU=1: Partner Status Table (PST)
•File#1: File Directory (files and their extent pointers)
•File#2: Disk Directory
•File#3: Active Change Directory (ACD)
–The ACD is analogous to a redo log, where changes to the metadata are logged.
–Size=42MB * number of instances
File#4: Continuing Operation Directory (COD).
–The COD is analogous to an undo tablespace. It maintains the state of active ASM operations such as disk or datafile drop/add. The COD log record is either committed or rolled back based on the success of the operation.
•File#5: Template directory
•File#6: Alias directory
•11g, File#9: Attribute Directory
•11g, File#12: Staleness registry, created when needed to track offline disks
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