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Symptoms

When trying to drop a disk from a diskgroup with external redundancy, the following events occur:

- Getting error: ORA-15041: diskgroup space exhausted. Although there is much free space on diskgroup!
- Rebalance not completed and disk couldn't be dropped.
- Disk becomes is status HUNG.

When disk is undropped, then performing manual rebalance (using ALTER DISKGROUP REBALANCE) completes successfully, but data is not really evenly distributed among disks in the diskgroup (i.e. it seems a fake rebalance).

There might be other symptoms like:
- Many of the warning message below in the alert log of the ASM instance:
WARNING: allocation failure on disk for file xnum
- A resize of a datafile results in ORA-1237
- Errors extending objects (e.g ORA-1652, ORA-1654)

Cause

Data was not evenly distributed among disks even after manaul rebalance.
There might be inconsistency remaining in the metadata.

Solution

1- check and repair metadata inconsistency
SQL> Alter diskgroup check all repair;

2- Perform. manual rebalance
SQL> alter diskgroup rebalance power 11;

(we used power 11 to make rebalance as fast as possible)

3- Monitor v$asm_operation and wait until rebalance is complete

4- Check v$asm_disk to see if data is now balanced across disks.

5- If data is now balanced correctly, then try to drop the disk you want to drop.

References

NOTE:419014.1 - ORA-15041 V$ASM_DISK Shows HUNG State for Dropped Disks