We have an issue with Windows XP SP3 VMs on VMWare ESXi 4.1.0 (the free version): They sometimes seem to "pause" for several minutes. This happens rarely (maybe once a month per VM, at least noticed only that often), but still is an issue for us. It happens for three different but similar VMs on three pretty different hosts (different hardware). I have the feeling that the "pausing" is not actually the CPU blocking, but probably the harddisks, but not 100% sure. The servers have one IDE disk (C:) and one SCSI (D:) and it might be either of the two. I have seen scheduled tasks simply not starting for up to 9 minutes and then running normally again with normal speed. They were totally blocked. This is not a load issue, the VMWare hosts have average load and the VMs in question already have reserved CPU resources plus high priorities for CPU and disk. The Windows boxes run mainly MySQL, Tomcat, FileZilla server, Cygwin stuff, Java + R applications, VMWare client, Elusiva Terminal Server pro, Nagios client. Not sure if this might be related with any of that software (e.g. Elusiva). Trying to debug this, there was nothing visible in Windows Event log, other logs in C:\Windows, VMWare events etc. Unfortunately the vmware.log file ends with "Log throttled". We found that we ran into 2 VMWare bugs there: The VMWare client writes lots on bogus messages in the vmware.log, which we now disabled (log level error setting) plus the bug that VMWare does not unthrottle the log (at least so far despite VM reboots). I know there is not much guidance and that may also be the reason why I so far didn't find anything related on the web or on ServerFault, but maybe some of this rings a bell with someone? Or please direct me to what more info to post. I hope that the vmware.logs get unthrottled eventually (can't easily restart the hosts at the moment). Thanks for any input!