You might get an error during the Syneto ESXi upgrade with:
[InstallationError] [Errno 28] No space left on device vibs = VMware_locker_tools-light_18.104.22.16803738-16701467 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.