You might get an error during the Syneto ESXi upgrade with:

 [InstallationError]
 [Errno 28] No space left on device
       vibs = VMware_locker_tools-light_11.1.1.16303738-16701467
 Please refer to the log file for more details.

Swap size is too small for temporary actions so you need to add a local datastore for swap.

To do that you need to login into your ESXi hypervisor UI. 

Go to Monitor -> System -> Swap and Edit Settings.

Change from none to local datastore (in our case datastore1)

Try again to run the update.

https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.resmgmt.doc/GUID-C0DBB2A3-4B44-45BE-927E-10EEB2EB8CBE.html