ESXi 6.x host is disconnected from vCenter Server

VMware vSphere ESXi

ESXi host showing as Disconnected in vCenter Server is a known issue in ESXi 6.x.

Symptoms:

ESXi hosts appear as Not Responding in vCenter Server.
Running esxcli commands on the ESXi host fail with the error:

Error interacting with configuration file /etc/vmware/lunTimestamps.log: Timeout while waiting for lock, /etc/vmware/lunTimestamps.log.LOCK, to be released. Another process has kept this file locked for more than 30 seconds. The process currently holding the lock is smartd(PID). This is likely a temporary condition. Please try your operation again.

Note: PID is the process ID for the smartd service.
In the /var/log/hostd.log file, you see entries similar to:

Error interacting with configuration file /etc/vmware/lunTimestamps.log: Timeout while waiting for lock, /etc/vmware/lunTimestamps.log.LOCK, to be released. Another process has kept this file locked for more than 30 seconds. The process currently holding the lock is smartd(PID). This is likely a temporary condition. Please try your operation again.
In the /var/log/syslog.log file, you see entries similar to:

<YYYY-MM-DD><time> Unknown: out of memory [PID]</time>

Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.

This issue is resolved in:

For ESXi 6.0: ESXi 6.0 Patch Release ESXi600-201706001, available at VMware Patch Downloads. For more information, see VMware ESXi 6.0, Patch Release ESXi600-201706001 (2149954).
For ESXi 6.5: ESXi 6.5 Patch Release ESXi650-201703001, available at VMware Patch Downloads. For more information, see VMware ESXi 6.5, Patch Release ESXi650-201703001 (2148989).

Note: For more information on downloading patch, see How to download patches in Customer Connect (1021623).

To work around this issue, disable smartd daemon on the host.

To disable smartd daemon:

Connect to the affected ESXi host with an SSH session. For more information, see Using ESXi Shell in ESXi 5.x and 6.0 (2004746).
Run this command to stop the smartd service:

/etc/init.d/smartd stop
Run this command to stop the smartd service from starting on reboot:

chkconfig smartd off