How to drop a disk from an ASM disk group in Oracle

Drop a disk from an ASM disk group. ASM rebalances the data off the disk first. Run connected to the ASM instance AS SYSASM.

The disk is not released until the rebalance finishes and V$ASM_DISK no longer shows it. Removing the physical disk before that risks data loss. Make sure the group has enough free space to hold the evacuated data.

ALTER DISKGROUP &&dg_name
  DROP DISK &&disk_name
  REBALANCE POWER 4;

-- Watch the rebalance to completion (read-only)
SELECT operation, state, power, est_minutes
FROM   v$asm_operation;

-- The disk is fully removed when this returns no rows
SELECT name, path, header_status
FROM   v$asm_disk
WHERE  name = UPPER('&disk_name');