The VM is inaccessible as vSAN host offline abnormal

Products

• VMware vSAN
• VMware vSAN 7.x
• VMware vSAN 8.x

Issue/Introduction

In vSAN cluster, one host entered into Maintenance Mode with default option "Ensure Accessibility".
Soon after, another host was offline abnormally, for example: PSoD, hardware failure ,abnormal reboot.
The VM use the default vSAN storage policy (FTT=1).
Some VMs dropped into inaccessible state.

# esxcli vsan debug object health summary get

Health Status                                              Number Of Objects
---------------------------------------------------------  -----------------
remoteAccessible                                                           0
inaccessible                                                               5
reduced-availability-with-no-rebuild                                       0
reduced-availability-with-no-rebuild-delay-timer                           0
reducedavailabilitywithpolicypending                                       0
reducedavailabilitywithpolicypendingfailed                                 0
reduced-availability-with-active-rebuild                                   0
reducedavailabilitywithpausedrebuild                                       0
data-move                                                                  0
nonavailability-related-reconfig                                           0
nonavailabilityrelatedincompliancewithpolicypending                        0
nonavailabilityrelatedincompliancewithpolicypendingfailed                  0
nonavailability-related-incompliance                                       0
nonavailabilityrelatedincompliancewithpausedrebuild                        0
healthy                                                                  522

Environment

vSAN 7.x

vSAN 8.x

Cause

The VM objects were inaccessible as it suffered more failures than the redundancy.

• For the default policy "FTT=1", there were two data copies for each vSAN object in the health status.
•  When the first host entered into Maintenance Mode with "Ensure Accessibility",
    Some VMs with default policy "FTT=1" should lost redundancy. The amount of active data copy decreased to one.
•  When the second host changed to offline abnormally, the VM should be inaccessible as neither data copy was accessible.
   The VM didn't resumed even the first host had exited the Maintenance Mode.
   For the affected VM, the latest data copy was located the second host.

Resolution

1.If the failures of second host are not temporary,
  it's suggested to work on the underlying root cause,
  such as a failed ESXi hosts, failed network, removed disks and so on. 
  as quickly as possible to restore availability. 

2. For any critical VM, there are some suggestions to reduce the risk of double failures.

• Increasing tolerate level for the VM.
  For example, choosing a storage policy with "FTT=2".
• Entering into Maintenance Mode with the option "Full data migration".