Hi,
usually, the VM's does have some kind of disk timeout timer, i. e., for Windows this timeout value must be set to 60 sec.
This will usually be done when you install the VMware tools.
So when you're VM is unable to access a disk, it will retry it for 60 sec before it will report an error.
During this timeframe, the ESX server must handle the error condition to allow the VM to keep alive.
Any IO operation from an affected VM will be freezed until the error condition is solved.
Hope this helps a bit.