ASM磁盘组支持动态扩展，我们可以向现有的磁盘组动态加入新的磁盘，新磁盘加入后，Oracle通过后台RBAL进行Rebalance，将当前的数据均衡到新增加的磁盘上。Drop磁盘亦会Rebalance。
asm_power_limit参数用于控制Rebalance的速度，取值 1～11，数字越大，平衡速度越快，默认值是1。如果该数字很大，则可能因为Rebalance而影响性能。也可以通过在alter diskgroup .. add/drop disk命令中通过rebalance power [1~11]选项控制Rebalance的速度。
Ora10gASM-> sqlplus "/ as sysdba"
SQL*Plus: Release 10.2.0.1.0 - Production on Wed May 28 20:11:39 2008
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> col name format a15
SQL> col failgroup format a20
SQL> col path format a30
SQL> select name,failgroup,path from v$asm_disk;
NAME FAILGROUP PATH
--------------- -------------------- ------------------------------
ORCL:VOL4
VOL1 VOL1 ORCL:VOL1
VOL2 VOL2 ORCL:VOL2
VOL3 VOL3 ORCL:VOL3
SQL> select name from v$asm_diskgroup;
NAME
---------------
DATA
FRA
DATA2
SQL> select name,total_mb,free_mb from v$asm_disk;
NAME TOTAL_MB FREE_MB
--------------- ---------- ----------
511 0
VOL1 4094 1872
VOL2 4094 3867
VOL3 511 358
加入磁盘ORCL:VOL4到DATA2磁盘组
SQL> alter diskgroup DATA2 add disk 'ORCL:VOL4' rebalance power 1;
Diskgroup altered.
Rebalance后磁盘空间使用情况
SQL> select name,total_mb,free_mb from v$asm_disk;
NAME TOTAL_MB FREE_MB
--------------- ---------- ----------
VOL1 4094 1872
VOL2 4094 3867
VOL3 511 433
VOL4 511 434
Drop 磁盘操作
SQL> alter diskgroup DATA2 drop disk 'ORCL:VOL4' rebalance power 11;
alter diskgroup DATA2 drop disk 'ORCL:VOL4' rebalance power 11
*
ERROR at line 1:
ORA-15032: not all alterations performed
ORA-15054: disk "ORCL:VOL4" does not exist in diskgroup "DATA2"
SQL> select name,failgroup,path from v$asm_disk;
NAME FAILGROUP PATH
--------------- -------------------- ------------------------------
VOL1 VOL1 ORCL:VOL1
VOL2 VOL2 ORCL:VOL2
VOL3 VOL3 ORCL:VOL3
VOL4 VOL4 ORCL:VOL4
SQL> alter diskgroup DATA2 drop disk 'VOL4' rebalance power 11;
Diskgroup altered.
SQL> select name,failgroup,path from v$asm_disk;
NAME FAILGROUP PATH
--------------- -------------------- ------------------------------
VOL1 VOL1 ORCL:VOL1
VOL2 VOL2 ORCL:VOL2
VOL3 VOL3 ORCL:VOL3
VOL4 VOL4 ORCL:VOL4
SQL> select name,total_mb,free_mb from v$asm_disk;
NAME TOTAL_MB FREE_MB
--------------- ---------- ----------
511 0
VOL1 4094 1872
VOL2 4094 3867
VOL3 511 358
SQL> select name,failgroup,path from v$asm_disk;
NAME FAILGROUP PATH
--------------- -------------------- ------------------------------
ORCL:VOL4
VOL1 VOL1 ORCL:VOL1
VOL2 VOL2 ORCL:VOL2
VOL3 VOL3 ORCL:VOL3
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
Ora10gASM-> ps -ef | grep rbal
oracle 5291 1 0 19:30 ? 00:00:03 asm_rbal_+ASM
oracle 5469 1 0 19:44 ? 00:00:01 ora_rbal_benbo
oracle 5970 4700 0 20:25 pts/1 00:00:00 grep rbal
Ora10gASM->
