思路分析：
1、發現數據庫宕機，檢查alert日志發現如下出現控制文件：I/O錯誤
Thu Apr 11 06:40:14 2019
WARNING: Read Failed. group:2 disk:1 AU:675 offset:16384 size:16384
WARNING: failed to read mirror side 1 of virtual extent 0 logical extent 0 of file 260 in group [2.3852408873] from disk DATA_0001 allocation unit 675 reason error; if possible, will try another mirror side
Errors in file /u01/app/oracle/diag/rdbms/jsswgsjk/jsswgsjk1/trace/jsswgsjk1_ckpt_93628.trc:
ORA-00202: control file: '+DATA/jsswgsjk/controlfile/current.260.998936297'
ORA-15081: failed to submit an I/O operation to a disk
ORA-27072: File I/O error
Linux-x86_64 Error: 5: Input/output error
Additional information: 4
Additional information: 1382432
Additional information: -1
Thu Apr 11 06:40:15 2019
WARNING: Read Failed. group:2 disk:1 AU:675 offset:65536 size:16384
2、檢查ASM日志
-------發生磁盤超時，開始dimountOCR
Thu Apr 11 06:39:29 2019
NOTE: process _b000_+asm1 (31654636) initiating offline of disk 0.3671375779 (OCR_0000) with mask 0x7e in group 3
NOTE: process _b000_+asm1 (31654636) initiating offline of disk 1.3671375780 (OCR_0001) with mask 0x7e in group 3
NOTE: process _b000_+asm1 (31654636) initiating offline of disk 2.3671375781 (OCR_0002) with mask 0x7e in group 3
NOTE: checking PST: grp = 3
GMON checking disk modes for group 3 at 13 for pid 67, osid 31654636
ERROR: no read quorum in group: required 2, found 0 disks
NOTE: checking PST for grp 3 done.
NOTE: initiating PST update: grp = 3, dsk = 0/0xdad4bfa3, mask = 0x6a, op = clear
NOTE: initiating PST update: grp = 3, dsk = 1/0xdad4bfa4, mask = 0x6a, op = clear
NOTE: initiating PST update: grp = 3, dsk = 2/0xdad4bfa5, mask = 0x6a, op = clear
GMON updating disk modes for group 3 at 14 for pid 67, osid 31654636
ERROR: no read quorum in group: required 2, found 0 disks <<<< 0個磁盤可訪問。
Thu Apr 11 06:39:29 2019
解決方案：
1、綜合以上信息分析，故障分析總結如下：
Oracle RAC ASM管理磁盤組有一種特有的心跳磁盤監控’ASM PST heartbeat’，這個監控是在oracle 11.2.0.3之后出現，系統默認設至是15s，到12.1.0.2之后oracle把默認值改為了120s。
這個PST heartbeat：往往發生在IO閃斷/繁忙/CPU繁忙時，PST檢測到同步延遲超過"_asm_hbeatiowait"值時，會通知ORACLE ASM INSTANCE dismount disk group，造成ASM instance disk group offline。一般Normal Redundancy或者High Redundancy策略下，超過半數的disk group offline就會造成Rack腦裂。
我們任何的升級在鏈路切換中，PP一般會hold住 IO 15秒鍾左右再恢復，很大可能性會引起上述timeout問題，在升級之前強烈建議更改此參數值到120。
具體的檢查這個參數的辦法如下，修改為120s后，為確保設置生效，需要重啟CRS服務。
2、檢查參數 “_asm_hbeatiowait” 的值：（檢查為：15）
select ksppinm as "hidden parameter", ksppstvl as "value"
from x$ksppi
join x$ksppcv
using (indx)
where ksppinm like '\_%' escape '\'
and ksppinm like '%asm_hb%'
order by ksppinm;
3、修改方案，在ASM實例下調整
alter system set "_asm_hbeatiowait"=120 scope=spfile;
注意重啟ASM或者CRS