Oracle ASM disk resync allows multiple disks to be brought online simultaneously or to otherwise control the speed of the resync operation. Oracle ASM disk resync now has a Resync Power Limit to control resync parallelism and, therefore, improve performance. Disk Resync Checkpoint allows for faster recovery from instance failures by allowing the resync to resume from where it was interrupted or stopped instead of starting from the beginning.
This enhancement provides faster recovery from instance failure and faster resync performance overall.
在此之前只有rebalance时才能指定并行度，现在可以再online磁盘的时候指定并行度加快online速度，并且也可以通过查询v$asm_operation视图来查看所需的大概时间。磁盘同步检查点更是加快了同步的速度，比如，你在online磁盘的时候，突然窗口关掉了，那么要是在12c之前的版本，你只能重新online。那么在12c中，Oracle会在online过程中，自动创建一个同步检查点，那么即使窗口关了，那么也会从最新的检查点开始再同步，很明显这个大大加快了同步的速度。
语法：
alter diskgroup DATA online disk DATA001 power 4; --范围(0--1024)
查看同步预估剩余时间：
Select est_minutes from v$asm_operation;
参考文档：
http://docs.oracle.com/database/121/SQLRF/statements_1009.htm#BABEFCHE
http://docs.oracle.com/database/121/OSTMG/GUID-6BB31112-8687-4C1E-AF14-D94FFCDA736F.htm#OSTMG10070