In the previous post of “11gR2 ASM – Inside story – Part4 (ASM Preferred Read Failure Group)”, we have seen how to configure the ASM instance with a list of preferred disk failure group names to use when accessing ASM disks.
In this section, we will see how to access to the database file managed within the ASM instance via OS command.
In this note, we will use the undocumented X$KFFXP table, which contains the physical allocation table for files managed via an ASM instance.
In this demonstration, we will try to read the content of the spfile managed by the ASM instance, using the dd command.
First, we query the view V$ASM_FILE to get the diskgroup number and the file number. Then, we will get the disk number where the spfile is located (Query the view X$KFFXP). Once we get the disk numbers, we query the view v$asm_disk to get the OS path, where exactly the spfile is located,. In the end, using the OS command “dd”, we will read the 10 first lines of the spfile, starting from the offset 717M, which is the result shown in AU_KFFXP for the disk number 0.
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