Scenario: When unmounting a datastore I got the following error on an ESXi 5.1 hosts: The vSphere HA agent on host ‘<host>’ failed to quiesce file activity on datastore ‘/vmfs/volumes/xxxxxxx-xxxxxxxxx-xxxxxxxxx-xxxxx’. To proceed with the operation to unmount or remove a datastore, ensure that the datastore is accessible, the host is reachable and its vSphere HA agent is running.
I had already gone through all the pre-reqs to ensure the datastore could be unmounted but I still got the above error. Under closer inspection of the HA cluster settings it appeared that I had “Select any of the cluster datastores taking into account my preferences” selected and the specific datastore unchecked. I decided to tick “Select on from my preferred datastores” instead and tried the unmount again. Successful this time!
Note: The above may be a red herring. I tried to unmount from another host and got the same result (2 other hosts allowed me to remove this without issue). To get around this I went to Inventory -> Hosts and Clusters -> chose the relevant host -> clicked Summary tab -> unmounted the datastore again. That seemed to work. Perhaps just a bug in vSphere 5.1 ?