No free space to rebalance ASM disk group

 

 To day we found below warning message from Exadata system:

Warning: Software Alert 92_1
Event Time	2025-01-23T16:19:57+06:00
Description	Insufficient free space to rebalance the ASM disk group: RECOC1
Affected Server	Name ******* Server Model Oracle Corporation ORACLE SERVER X9-2 Chassis Serial Number 2217XCD00X Release Version 24.1.5.0.0.241016 RPM Version 24.1.5.0.0.241016
Recommended Action	Please refer to MOS Doc 1551288.1

    

I am search  Chatgpt and found below solutions.

Rebalancing an ASM (Automatic Storage Management) disk group in Oracle is a process where the disk group redistributes data across its disks to ensure optimal space utilization, performance, and redundancy. This can happen when you add or remove a disk from the disk group, or after certain maintenance activities.

Here’s how you can rebalance an ASM disk group:

Steps to Rebalance an ASM Disk Group:

1. Check the Disk Group Status

   First, verify the status of your ASM disk group and ensure that it's healthy. You can use the following SQL query:

   sql
   SELECT name, state, total_mb, free_mb, usable_file_mb 
   FROM v$asm_diskgroup;
   

   This will give you the current status of the disk groups, including how much space is used and available.

2. Add or Remove Disks (Optional)

   If you’ve added or removed a disk, ASM will usually start the rebalance process automatically. For example, if you add a new disk to the disk group:

   sql
   ALTER DISKGROUP <diskgroup_name> ADD DISK '<disk_path>';
   

   Or to remove a disk:

   sql
   ALTER DISKGROUP <diskgroup_name> DROP DISK '<disk_name>';
   

   Once a disk is added or removed, ASM will begin the rebalance operation automatically.

3. Manually Initiate a Rebalance (If Needed)

   If you need to manually start the rebalance process (for example, if you're reorganizing data or after making changes like adding/removing disks), you can use the following SQL command:

   sql
   ALTER DISKGROUP <diskgroup_name> REBALANCE;
   

4. Monitor the Rebalance Process

   You can monitor the progress of the rebalance operation using the following query:

   sql
   SELECT * FROM v$asm_operation;
   

   This will show the status of any ongoing operations, including the rebalance process. You should see something like this:

   plaintext
   OPERATION_TYPE  | STATE   | PERCENT_COMPLETED
   ----------------------------------------------
   REBALANCE       | IN PROGRESS | 45
   

   The PERCENT_COMPLETED column will indicate the progress of the rebalance.

5. Check Disk Group After Rebalance

   After the rebalance completes, you can check the disk group status again to ensure that the rebalance operation has completed successfully and that space is optimally distributed:

   sql
   SELECT name, state, total_mb, free_mb, usable_file_mb 
   FROM v$asm_diskgroup;
   

6. Cancel a Rebalance (Optional)

   If you need to cancel the rebalance operation for any reason (e.g., due to performance impact or maintenance), you can do so using:

   sql
   ALTER DISKGROUP <diskgroup_name> REBALANCE CANCEL;
   

   Keep in mind that canceling the rebalance might leave data not optimally distributed until you rerun the operation.

Important Considerations:

• Performance Impact: Rebalancing can be resource-intensive and affect the performance of the system. It is typically recommended to run the rebalance operation during off-peak hours.

• Rebalance Speed: The speed of the rebalance process depends on the amount of data to be redistributed and the system's available resources. You can control the rebalance speed using the POWER parameter:

  sql
  ALTER DISKGROUP <diskgroup_name> REBALANCE POWER <value>;
  

  Values for POWER range from 1 to 11 (where 1 is the slowest and 11 is the fastest).

  Example to rebalance with higher speed:

  sql
  ALTER DISKGROUP <diskgroup_name> REBALANCE POWER 8;
  

• Rebalance During Maintenance: If you're removing a disk for maintenance, ensure you let ASM properly rebalance the data before taking any disks offline. This prevents data loss and ensures redundancy.

By following these steps, you should be able to successfully initiate and monitor a rebalance operation in Oracle ASM.

Let me know if you need further assistance!