When you upgrade virtual machines, the required downtime depends on the guest operating system.

When you upgrade VMware Tools, expect the following downtime:

No downtime is required for vCenter Server.

No downtime is required for ESXi hosts.

You must reboot Microsoft Windows virtual machines at the end of the upgrade procedure, or later, for the upgrade take effect.

On Windows guest operating systems, you must reboot the virtual machine three times when you upgrade VMware Tools and the virtual hardware.

For NetWare and Solaris guest operating systems, no reboot is required at the end of the procedure.

For Linux guest operating systems, you must restart the virtual machine. See Knowledge Base article http://kb.vmware.com/kb/2050364.

During the virtual hardware upgrade, you must shut down the virtual machine for all guest operating systems.

Virtual Machine Downtime by Guest Operating System summarizes the downtime required by guest operating system and by upgrade operation.

Virtual Machine Downtime by Guest Operating System

Guest Operating System

Upgrade VMware Tools

Upgrade Virtual Hardware

Linux

No downtime.

Downtime for shut down and power on of virtual machine.

NetWare

No downtime.

Downtime for shut down and power on of virtual machine.

Solaris

No downtime.

Downtime for shut down and power on of virtual machine.

Microsoft Windows

Downtime for reboot of guest operating system.

Downtime for shut down and power on of virtual machine.