Intermittent NFS All Paths Down on ESXi 5.5 U1 upgrade

Those of you using NFS storage and planning to upgrade to the latest version of vSphere – 5.5 U1 – please hold off your upgrades as there is a bug within the code which is currently causing issues on paths to NFS volumes.

The bug causes the intermittent loss of connectivity, which can lead to an “All Paths Down” error to your NFS storage! During the disconnects VMs will appear frozen and the NFS datastores may be greyed out. This appears to impact all storage vendors and all environments on 5.5. U1 accessing NFS…..!!
Obviously the loss of a path will impact IOs from VMs to datastores…… and this can result in BSODs for Windows VMs and filesystems becoming read only for Linux VMs (or even kernel panics)!

The recommendation at this point is not to upgrade to vSphere 5.5 U1 and stay on vSphere 5.5 GA. If you have upgraded to 5.5 U1 then you may need to downgrade back to 5.5GA.

More information can be found here:

I suggest you subscribe to the KB in order to get an update as to when this bug is resolved.


Have a look at William Lam’s blog regarding setting up alarms within vCenter Server that could help alert when these APD issues occur:

How to create vCenter Alarm to alert on ESXi 5.5u1 NFS APD issue?


Obviously the main reason for upgrading to 5.5 U1 was to patch the Heartbleed vulnerability within OpenSSL, VMware are informing customers not to upgrade but to install security patches to address the Heartbleed vulnerability…. More info on this process can be found here:

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