12c中asm得到了很多增强，这里列举几点：
1. Estimate Work
在12c中，你可以用explain work for xxxx 和 v$asm_esitmate视图，来看有多少个block会参与到这项改变中。
[oracle@12102-rac1 dev]$ sqlplus "/ as sysasm"
SQL*Plus: Release 12.1.0.2.0 Production on Thu Feb 18 12:00:14 2016
Copyright (c) 1982, 2014, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Real Application Clusters and Automatic Storage Management options
SQL>
SQL>
SQL> select * from V$ASM_ESTIMATE;
no rows selected
SQL> explain work for alter diskgroup dg_data drop disk DG_DATA_0003;
Explained.
SQL> select * from V$ASM_ESTIMATE;
GROUP_NUMBER STATEMENT_ID TIMESTAMP EST_WORK CON_ID
------------ ------------------------------ ------------------- ---------- ----------
1 2016-02-18 12:00:33 4565 0
SQL>
GROUP_NUMBER OPERA PASS STAT POWER ACTUAL SOFAR EST_WORK EST_RATE EST_MINUTES ERROR_CODE CON_ID
------------ ----- --------- ---- ---------- ---------- ---------- ---------- ---------- ----------- -------------------- ----------
1 REBAL REBALANCE RUN 1 1 120 4565 1092 4 0
1 REBAL COMPACT WAIT 1 1 0 0 0 0 0
Elapsed: 00:00:00.00
SQL>
SQL>
SQL> /
GROUP_NUMBER OPERA PASS STAT POWER ACTUAL SOFAR EST_WORK EST_RATE EST_MINUTES ERROR_CODE CON_ID
------------ ----- --------- ---- ---------- ---------- ---------- ---------- ---------- ----------- -------------------- ----------
1 REBAL REBALANCE RUN 1 1 4469 4565 857 0 0
1 REBAL COMPACT WAIT 1 1 0 0 0 0 0
Elapsed: 00:00:00.00
SQL>
SQL>
SQL>
SQL> /
GROUP_NUMBER OPERA PASS STAT POWER ACTUAL SOFAR EST_WORK EST_RATE EST_MINUTES ERROR_CODE CON_ID
------------ ----- --------- ---- ---------- ---------- ---------- ---------- ---------- ----------- -------------------- ----------
1 REBAL REBALANCE DONE 1 0
1 REBAL COMPACT WAIT 1 0
Elapsed: 00:00:00.00
SQL>
2. fast disk resync：（非external冗余）
原来11g中的fast resync比较适用于单个disk的损坏，或者损坏只是一段很小的时间（默认repair time是3.6小时）。如果损坏了很长的时间，或者有很多disk都发生了损坏。online disk的操作由于是单线程的，往往会很慢。
在12c了，这个已经是多线程处理了。可以使用
alter diskgroup XX online disk YYY power ;
或者
asmcmd online -G XX -D YY -power ;
3. ACFS支持放database datafile
ACFS Support On OS Platforms (Certification Matrix). (Doc ID 1369107.1)
ACFS Advanced Features Platform Availability – Minimum Version
4. 已经可以rename disk：