错误：unmount _varfs：无法卸载/var文件系统

在ONTAP 从9.1P13升级到9.3P21期间、节点无法启动、并出现类似错误：

REBOOTING TO LOAD NEW NVRAM FIRMWARE...
WARNING: Aborting boot (sending SIGTERM to parent)!
/etc/rc.d/netapp_frulog: cannot create /var/log/netapp_frulog.log: No such file or directory
[Feb 16 04:17:31]: 0x801e04200: 0: NOTICE: RpcConnectionCache: markFailure: markFailure: New Quarantine for localhost:536873474(spmd)/1[tcp]{fffffffd|ffffffff} with timeout(20.000s) Reason:: RPC: Unknown host
/etc/rc.shutdown: WARNING: $vmtools_enable is not set properly - see rc.conf(5).
/etc/rc.shutdown: WARNING: $xinetd_enable is not set properly - see rc.conf(5).
.: cannot open /etc/rc.conf: No such file or directory
/etc/rc.d/netapp_mgmt: cannot create /var/log/netapp_mgmt.log: No such file or directory
/etc/rc.d/netapp_fpolicy: cannot create /var/log/netapp_fpolicy.log: No such file or directory
/etc/rc.d/netapp_mdns: cannot create /var/log/netapp_mdns.log: No such file or directory
/etc/rc.d/netapp_mes: cannot create /var/log/netapp_mes.log: No such file or directory
/etc/rc.shutdown: WARNING: write failed (read-only fs?)
.
Terminated
varfs_backup_restore: /var/VERSION missing! /var is not backed up to the boot device.
ERROR: unmount_varfs: Failed to umount /var file system.
Uptime: 3m4s
System rebooting...