某客戶運維人員，根據業務需求，本意修改Oracle資料庫 記憶體引數，因操作不當，修改成asm例項引數，因記憶體引數值過大，造成asm例項無法啟動， 具體處理過程如下：

檢查叢集日誌，發現如下資訊,顯示所有磁碟組無法mount

```
2021-06-19 09:15:36.133 [ORAROOTAGENT(3375)]CRS-5019: All OCR locations are on ASM disk groups [CRS], and none of these disk groups are mounted. Details are at "(:CLSN00140:)" in "/u01/app/grid/diag/crs/rac19c/crs/trace/ohasd_orarootagent_root.trc".
2021-06-19 09:23:38.949 [OCRCHECK(8885)]CRS-1013: The OCR location in an ASM disk group is inaccessible. Details in /u01/app/grid/diag/crs/rac19c/crs/trace/ocrcheck_8885.trc.
2021-06-19 09:23:50.732 [OCRCONFIG(8932)]CRS-1013: The OCR location in an ASM disk group is inaccessible. Details in /u01/app/grid/diag/crs/rac19c/crs/trace/ocrconfig_8932.trc.

```

檢視asm警告日誌,發現memory_target 報警告
```
WARNING: You are trying to use the MEMORY_TARGET feature. This feature requires the /dev/shm file system to be mounted for at least 17179869184 bytes. /dev/shm is either not mounted or is mounted with available space less than this size. Please fix this so that MEMORY_TARGET can work as expected. Current available is 4093005824 and used is 86016 bytes. Ensure that the mount point is /dev/shm for this directory.
2021-06-19T09:40:16.086198+08:00
WARNING: You are trying to use the MEMORY_TARGET feature. This feature requires the /dev/shm file system to be mounted for at least 17179869184 bytes. /dev/shm is either not mounted or is mounted with available space less than this size. Please fix this so that MEMORY_TARGET can work as expected. Current available is 4093005824 and used is 86016 bytes. Ensure that the mount point is /dev/shm for this directory.
WARNING: Automatic memory management feature on ASM needs /dev/shm to be mounted and sized alteast to the value of MEMORY_TARGET 17179869184. Falling back to manual memory management on the ASM instance.
```

通過日誌查詢，發現在一個月前有人修改過該引數。目前asm無法啟動，無法訪問磁碟組。通過手動編輯pfile檔案啟動asm例項

``` shell
#指定pfile檔案啟動ASM(指定近期SPFILE，確保只修正memory_max_target memory_target )
vi /tmp/pfile
spfile="+CRS/rac19c-cluster/ASMPARAMETERFILE/registry.253.1075633673"
*.memory_target=1073741824
*.memory_max_target=1073741824

#啟動後調回正確的引數
[grid@rac19c ~]$ sqlplus / as sysasm
SQL> startup pfile='/tmp/pfile';
SQL>alter system set memory_max_target=1073741824 scope=spfile;
SQL>alter system set memory_target =1073741824 scope=spfile;

#重啟叢集，驗證是否正常 root
./crsctl start has

#通過以下命令檢視，叢集正常
crsctl stat res -t
```

至此問題解決，建議在做資料庫系統相關引數更改時，確認修改是否正確。

【ASM】RAC19C因引數設定不當，asm無法啟動

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