terminating the instance due to error 471/495

一套12C的数据库2节点RAC集群，节点2被down了，查看alertlog，报错如下：

2021-06-16T01:26:16.516936+08:00
Thread 2 advanced to log sequence 8611 (LGWR switch)
  Current log# 4 seq# 8611 mem# 0: +DATA/CB2QDB/ONLINELOG/group_4.305.992195801
  Current log# 4 seq# 8611 mem# 1: +DATA/CB2QDB/ONLINELOG/group_4.306.992195809
2021-06-16T01:26:16.852672+08:00
Archived Log entry 16829 added for T-2.S-8610 ID 0x643dd214 LAD:1
2021-06-16T01:27:09.344853+08:00
Instance Critical Process (pid: 34, ospid: 60840, DBW1) died unexpectedly
PMON (ospid: 60735): terminating the instance due to error 471
2021-06-16T01:27:12.685143+08:00
Instance terminated by PMON, pid = 60735

可见DBW1死掉了，没有更多信息描述。
查看grid日志，那个时刻的信息如下：

2021-06-16T01:27:06.031574+08:00
NOTE: ASM client -MGMTDB:_mgmtdb:cb2qdb disconnected unexpectedly.
NOTE: check client alert log.
2021-06-16T01:27:06.431417+08:00
Dumping diagnostic data in directory=[cdmp_20210616012706], requested by (instance=0, osid=9777), summary=[trace bucket dump request (kfnclDelete0)].
2021-06-16T01:27:07.537686+08:00
NOTE: ASMB process exiting, either shutdown is in progress or foreground connected to ASMB was killed.
NOTE: ASMB0 clearing idle groups before exit
2021-06-16T01:27:08.443825+08:00
Instance Critical Process (pid: 6, ospid: 76748, GEN0) died unexpectedly
PMON (ospid: 76720): terminating the instance due to error 495
2021-06-16T01:27:09.630299+08:00
Instance terminated by PMON, pid = 76720

可见那个时刻asm实例挂掉了，导致了DBW1死掉了。
关于471错误，在MOS关于这个错误有明确的描述，(Doc ID 1622379.1)，仅供参考。
此处的错误根源在于495，MOS给出的原因和解决方案很明确，如下：
PMON (ospid: nnnn): Terminating the Instance Due to Error 495 (Doc ID 2584936.1)

CAUSE:
Extending FS where datafiles exist.

Sep 3 23:26:18 cmstashdbl02 kernel: [51963237.523394] EXT4-fs warning (device dm-8): ext4_resize_begin:44: There are errors in the filesystem, so online resizing is not allowed
Sep 3 23:26:18 cmstashdbl02 kernel: [51963237.523394]

SOLUTION：
Check with os/storage admin.

问题是，6月16日凌晨那个时间点，谁在做存储的操作了？
我们看到，在这之前，有一个关键的操作信息，即：
NOTE: ASM client -MGMTDB:_mgmtdb:cb2qdb disconnected unexpectedly.
NOTE: check client alert log.
查看/u01/app/grid/diag/rdbms/mgmtdb/-MGMTDB/trace/alert-MGMTDB.log，可见如下信息：

2021-06-16T01:27:04.310472+08:00
License high water mark = 19
2021-06-16T01:27:04.310951+08:00
USER (ospid: 10795): terminating the instance
2021-06-16T01:27:07.315957+08:00
Instance terminated by USER, pid = 10795

就这么多信息，这个12c数据库当时还被迫装了这个mgmtdb，关于这个mgmtdb，现在实在不想去看那些文档了，先这样吧，oracle它奶奶个腿儿
知道了来龙去脉，修改了一些后来不知被谁改错的系统配置如sshd、limits等，强行关闭半死不活的crs，重启即恢复正常。