某10.2.0.5 ASM系统由于存储故障导致normal redundancy diskgroup中的4个failgroup中的2个failgroup的ASM DISK均无法访问，在10g中若ASM disk无法访问将直接将disk drop出diskgroup中。
报错如下：
Sat Nov 15 17:05:36 CST 2013 WARNING: PST-initiated drop disk 1(739802527).1(3915943320) WARNING: PST-initiated drop disk 1(739802527).3(3915943321) Sat Nov 15 17:05:36 CST 2013 NOTE: PST update: grp = 1 Sat Nov 15 17:05:36 CST 2013 ERROR: too many offline disks in PST (grp 1) Sat Nov 15 17:05:36 CST 2013 ERROR: ORA-15066 signalled during reconfiguration of diskgroup DATADG NOTE: requesting all-instance membership refresh for group=1 Sat Nov 15 17:05:36 CST 2013 NOTE: membership refresh pending for group 1/0x2c187d9f (DATADG) WARNING: rejecting drop force of disk number 1 WARNING: rejecting drop force of disk number 3 SUCCESS: refreshed membership for 1/0x2c187d9f (DATADG) Sat Nov 15 17:05:39 CST 2013 ERROR: PST-initiated disk drop failed Sat Nov 15 17:05:39 CST 2013 ERROR: PST-initiated MANDATORY DISMOUNT of group DATADG NOTE: cache dismounting group 1/0x2C187D9F (DATADG) Sat Nov 15 17:05:39 CST 2013 NOTE: halting all I/Os to diskgroup DATADG
由于是normal redundancy，所以只能丢失一个failgroup。ASM尝试drop 2个failgroup时会导致diskgroup被强制DISMOUNT，即PST-initiated MANDATORY DISMOUNT of group DATADG。
PST-initiated drop disk =》 PST初始化drop disk
ERROR: too many offline disks in PST (grp 1) ==> ASM认为若drop 这么多disk会导致丢失数据，所以是too many offline disk
WARNING: rejecting drop force of disk number 1
WARNING: rejecting drop force of disk number 3 ==> ASM拒绝drop这些disk
ERROR: PST-initiated disk drop failed==> PST初始化drop disk失败
ERROR: PST-initiated MANDATORY DISMOUNT of group ORADATA==》 强制dismount diskgroup
以上对于该asm diskgroup的维护将陷入死循环，即 mount diskgroup => 开始drop disk=> 由于drop disk过多 导致asm 强制dismount diskgroup => 人为再次手动mount diskgroup。 该ASM Diskgroup实际变得不可用了。
我们可以通过设置隐藏参数或者手动patch PST的方式来绕过该问题，具体需要了解ASM 底层数据结构的工程师现场根据实际情况实施，再次不再鏖述。
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