dismount ASM磁盘组，影响未使用的其它ASM磁盘组

# 问题概述
登录数据库,查看活动会话，发现大量library cache lock ,log file switch (archiving needed),归档失败，redo log无法重用。
# 问题原因
备份一体机每次备份后会DISMOUNT BAKDG，这个动作为导致数据库实例将"卸载"未使用的 ASM 磁盘组,ARCHDG在这种机制下被DISMOUNT,当数据库需要归档时会自动MOUNT ARCHDG，但由于备份一体机某磁盘块异常,无法mount磁盘，导致问题发生。
# 解决方案
临时处理：
1、把归档目录修改成数据磁盘的路径（ARCHDG -> DATADG）
2、等主机的同事修好磁盘
3、去除磁盘组的依赖关系
# 模拟故障

给我的虚拟机添加asm共享磁盘

datadg3是2021年的时候加上去的，bak是刚加上去的,

==为数据库添加磁盘组== https://www.modb.pro/db/334980
磁盘组使用情况，注意一下datadg3和bakdg的磁盘

因每次备份都需要先把bakdg的盘dismount ，在mount阶段
实验是我手动把bakdg的盘dismount，看看会不会有什么问题？
```
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.9.0.0.0
[grid@oadb1:/home/grid]$ sqlplus / as sysasm
SQL*Plus: Release 19.0.0.0.0 - Production on Mon Feb 21 14:03:31 2022
Version 19.9.0.0.0
Copyright (c) 1982, 2020, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.9.0.0.0
SQL> alter diskgroup BAKDG dismount;
Diskgroup altered.

```

db alert
```
2022-02-21T11:12:33.465395+08:00
Domain Action Reconfiguration started (domid 2, new da inc 2, cluster inc 4)
Instance 2 is attaching to domain 2
Global Resource Directory partially frozen for domain action
Non-local Process blocks cleaned out
Set master node info
Dwn-cvts replayed, VALBLKs dubious
All grantable enqueues granted
Domain Action Reconfiguration complete (total time 0.0 secs)
2022-02-21T11:12:36.346703+08:00
Domain Action Reconfiguration started (domid 3, new da inc 2, cluster inc 4)
Instance 2 is attaching to domain 3
Global Resource Directory partially frozen for domain action
Non-local Process blocks cleaned out
Set master node info
Dwn-cvts replayed, VALBLKs dubious
All grantable enqueues granted
Domain Action Reconfiguration complete (total time 0.1 secs)
2022-02-21T14:03:47.924817+08:00
SUCCESS: diskgroup DATADG3 was dismounted <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
```
发现DATADG3 自动dismount了 ，检查数据库磁盘的依赖关系
```
[grid@oadb1:/home/grid]$ srvctl config database -db jcoadb |grep "Disk Groups"
Disk Groups: DATADG,DATADG2,DATADG3,BAKDG,ARCHDG
```
去除依赖关系，在进行dismount操作，不会影响未使用的磁盘组
```
srvctl modify database -db priiboss -diskgroup 'DATADG,DATADG2,DATADG3,ARCHDG'

```