Rebalancing act in ASM for ACFS

Hi, who of you knows how ASM makes rebalancing act for ACFS? Below i’ll share you.

When I’ve got my first experience with ACFS my colleagues told me that the ASM makes rebalancing act per files but not per extents. As you know ASM provides storage for datafiles of RDBMS and makes different redundancy. And rebalancing act ASM makes for those files per extents. For example for normal redundancy diskgroup contains two extents, original and copy.

Diskgroup which contains ACFS makes rebalancing differently. But for me sounds very strange that the ASM makes rebalance per file for diskgroup which contains ACFS. For example we have OEBS and a lot of files from Concurrent Manager, so, ASM should synchronize all of them? Files have different sizes! Unfortunately i can’t find any clear information in documentation nevertheless i could talk with Bane Radulovic who is the author of blog ( and work in Oracle support.

As i could find out ASM makes rebalancing for ACFS per file but not those files which user can see in OS level!!! ASM makes rebalancing for special type files, ASMVOL files. It is very important! Sometimes we do rebalance for our diskgroup which contain ACFS and it always takes long time, a day probably +/-. You can tell me, hey it strange, because ASM have special mechanism which tracking which exactly extents had changed, Fast Mirror Resync. Yes ASM has this, but it not works for ASMVOL files. And ASM during operations ONLINE, REBALANCE read whole files of types ASMVOL. Engineers of Oracle had did already mechanism for tracking extents and it can appear in 12c.


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