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Don Burleson Blog 







Oracle ASM Dictionary Tables

Expert Oracle Database Tips by Donald BurlesonNovember 29, 2015

Question:  I understand that Automatic Storage Management (ASM) has an instance, but I cannot find the data dictionary tables for the ASM instance.  How do I tell what users are using the ASM instance?

Answer:  The ASM instance is not a full database instance, just the v$ and x$ memory structures needed to manage the file storage mapping between physical files and disk spindles. 

Remember, it's the whole database instance that connects to ASM, not any individual users or sessions.  

ASM has several v$ views (which are built from x$ fixed structures) that are used to manage the ASM instance file and disk details:

  • V$ASM_DISKGROUP (made from X$KFGRP): performs disk discovery and lists diskgroups

  •  V$ASM_DISKGROUP_STAT (made from X$KFGRP_STAT):  Lists the diskgroups

  • V$ASM_DISK (made from X$KFDSK and X$KFKID):  Contains disk details and usage statistiocs (e.g. ASM disk discovery).

  • V$ASM_DISK_STAT (made from X$KFDSK_STAT and X$KFKID):  Contains disk details and usage statistiocs

  • V$ASM_FILE (made from X$KFFIL):  Lists the ASM files

  • V$ASM_ALIAS (made from X$KFALS): Contains the ASM file and directory aliases.

  • V$ASM_CLIENT (made from (X$KFTMTA):  Lists all instances that are connected to ASM the ASM instance

  • V$OPERATION (made from X$KFGMG):  Contains the ASM file striping (re-balancing) operations

  • X$KFFXP:  Contains the extent mapping table for ASM files

Below we see the difference in contents for these v$ ASM view in the ASM instance and each database instance.  Note that the ASM instance does not have the row data as the database instance:

V$ View Name ASM Instance Database Instance
v$asm_alias Displays every alias for all disk groups that are  mounted by the ASM instance Empty view.
v$asm_client Displays every instance that is managed by the ASM instance. Displays an ASM instance ONLY if the database instance has open ASM files.
v$asm_disk Displays each physical disk spindle that is discovered by the ASM instance. Displays every disk for all ASM disk groups that are in use by the database instance.
v$asm_diskgtoup Displays every disk group that exists in the ASM instance (at discovery time). Displays ach disk group that is currently mounted to the ASM instance.
v$asm_file Displays all files within each disk group that is mounted by the ASM instance. Empty view.
 v$asm_operation Similar to v$session_longops, in function, v$asm_operation shows every file that is used in every long running operation executing within the ASM instance. Empty view.
v$asm_template Displays all templates within each disk group that is mounted by the ASM instance. Displays each template present or each mounted disk group, but only for disk groups that are in-use by the database instance.
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