Add disks to an ASM diskgroup

Command

-- Connect to the ASM instance (sqlplus / as sysasm)
ALTER DISKGROUP DATA ADD DISK
  '/dev/oracleasm/disks/DATA05' NAME DATA_0005,
  '/dev/oracleasm/disks/DATA06' NAME DATA_0006
  REBALANCE POWER 4;

What it does

Adds new disks to the DATA diskgroup and starts an automatic rebalance; capacity grows.

When to use it

When an ASM diskgroup starts filling up, or when expanding storage.

Caution

Requires the SYSASM privilege. Disk sizes should be similar. Rebalance creates I/O load; use a low POWER during busy hours.