Friday, December 20, 2013

Oracle ASM 11g R2 -- Oracle ADVM -- Differencies in Space Allocations for Different Versions

How Oracle ADVM Allocates Space for Volumes

All space allocation operations performed by Oracle ADVM are performed in Volume Allocation Units (VAU). VAU is the smallest allocation when a volume is created and smallest amount of space that can be added to a volume.

VAU value can be identified by the RESIZE_UNIT_MB column of the V$ASM_VOLUME view and by Resize Unit (MB) field of the VOLINFO asmcmd command.

VAU is calculated as multiplication of the STRIPE COLUMN value and the VOLUME EXTENT value 

The STRIPE COLUMN value is a number of stripes into which Oracle writes data in a round robin fashion. 

VOLUME EXTENT is bases on the allocation unit (AU) size of the disk group. In different versions VOLUME EXTENT value is differently calculated. 


In Oracle ASM and versions, VOLUME EXTENTS size is 64 times the allocation unit (AU) size of the disk group. 


In Oracle ASM the volume extent size is 8 MB if the disk group allocation unit (AU) is less than or equal to 8 MB. If the AU size is greater than 8 MB, then the Oracle ADVM volume extent size is equivalent to the disk group AU size.

Confusing Info in Oracle Documentation

Oracle Documentation incorrectly states the old style of determining volume extent size even for version The only place in Oracle Documentation where the correct info is provided for volume extent calculation is ASMCMD volcreate command description.


Anonymous said...

Thank you very much for this information, as I didn't find anywhere the explanation about the informations found in the documentation and in other doc ou places under Internet. Very useful

Aiglefin said...


Thank you for your explanation; It's a good summary.