ESXi Hosts Disconnected After Upgrade to 5.5


  •  VMware vCenter 5.5 Update 2
  • ESXi 5.5 Update 2
  • Hitachi HUS 110


  •  After the upgrade from ESXi 5.0 to 5.5 Update 2 ESXi host got disconnected from vCenter 
  • We were able to ping host however unable to access/add from vCenter
  • All the VMs on the host are also unresponsive.


After analyzing the logs  here is what we observed the problem was with ATS reservations failing (ATSF) for the LUNs

Step 1 – We verified ATSF values on ESXi Hosts using following procedure

enter command \”esxtop\” ,then:press u, next f, next o & p to select VAAISTATS and VAAILATSTATS/cmd fields.
check the value in column ATSF, ideally it should be \”0\”
if you see high number of ATSF it means you are having issue with failed ATS commands.

Step 2 – We verified and ensured that VAAI features are enabled on the ESXi  host from a console or SSH session using this command in the below mentioned KB Article

esxcli system settings advanced list -o /VMFS3/HardwareAcceleratedLocking

Step 3 – We checked storage and after analyzing logs with Hitachi we figured out that VAAI is not enabled by default in HUS 110

Also as per Hitachi it is a common error post upgrading to 5.5 and the VAAI is not enabled in HUS 110


 In order to enable VAAI feature on HUS 110 we need to enable following Host Mode options on the ESXi Host Groups using SNM2
  • Enable Unique Extended COPY Mode                   
  • Enable Unique Write Same Mode                           
  • Enable DP Depletion Detail Reply Mode   

 We enabled options and rebooted the hosts to release ATSF

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