Safely Remove a Used Disk from ASM DiskGroup in Oracle 19c RAC

How to Safely Remove a Used Disk from ASM DiskGroup in Oracle 19c RAC

In this post, I’m sharing a step-by-step process to safely remove a used disk from an ASM DiskGroup in Oracle 19c RAC without impacting data.

Removing a disk requires careful planning to maintain data integrity.

Key Points to Remember

  • Normal / High Redundancy: ASM automatically rebalances data across other disks.
  • External Redundancy: Ensure sufficient free space before removing the disk.
  • Free Space Check: FREE_MB should be greater than the space occupied by the disk to be dropped.
  • Mirroring Requirement: REQUIRED_MIRROR_FREE_MB should be less than FREE_MB to ensure proper mirroring.
  • Power Limit: Controls the speed of rebalancing.
    Example:

sqlCopyEditALTER DISKGROUP DATA REBALANCE POWER 7;

Recommended value: 1–11 (higher = faster but uses more resources). Maximum allowed: 0–1024 depending on system capacity.

Example Scenario

We have an ASM DiskGroup named +DATA with multiple disks. We want to remove disk DS8 safely.

1. Check Existing Disks in the DiskGroup

sqlCopyEditSET LINES 200COL name FORMAT a20COL path FORMAT a28COL total_mb FORMAT 99999COL free_mb FORMAT 99999 SELECT group_number, name, path, total_mb, free_mb, header_status, mount_status, stateFROM v$asm_diskWHERE group_number = (    SELECT group_number FROM v$asm_diskgroup WHERE name = ‘DATA’);

2. Check Redundancy Type & Space Availability

sqlCopyEditSELECT name, type, state, total_mb, free_mb, required_mirror_free_mb, usable_file_mbFROM v$asm_diskgroupWHERE name = ‘DATA’;

✅ Ensure FREE_MB > required space before proceeding.

3. Drop the Disk from ASM DiskGroup

sqlCopyEditALTER DISKGROUP DATA DROP DISK DS8;

Rebalancing will redistribute the data across remaining disks.

4. Monitor Rebalancing Progress

sqlCopyEditSELECT group_number, operation, state, est_minutesFROM v$asm_operation;

Wait until STATE = COMPLETED.

5. Verify DiskGroup After Rebalancing

sqlCopyEditSELECT name, total_mb, free_mbFROM v$asm_diskgroupWHERE name = ‘DATA’;

✅ Ensure DiskGroup is healthy and space is balanced.

6. Confirm Disk Removal

sqlCopyEditSELECT name, pathFROM v$asm_diskWHERE group_number = (    SELECT group_number FROM v$asm_diskgroup WHERE name = ‘DATA’);

If the disk is no longer listed → removal was successful.

7. Optional – Decommission the Physical Disk

Find disks with HEADER_STATUS = ‘FORMER’:

sqlCopyEditSELECT disk_number, name, pathFROM v$asm_diskWHERE header_status = ‘FORMER’;

Clear ASM metadata if reusing:

bashCopyEditdd if=/dev/zero of=/dev/sdX bs=1024 count=100asmcmd afd_label <disk> –init

Remove from ASM configuration:

bashCopyEditoracleasm deletedisk DS8

8. Final Check – Database Functionality

Ensure no performance issues or errors:

sqlCopyEditSELECT * FROM v$asm_diskgroup WHERE name = ‘DATA’;

✅ Conclusion: By following these steps, you can remove a disk from ASM safely without impacting database availability or data integrity.

 

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