Slow reboot of vSMP virtual machines on ESX

This issue occurs because of changes in the architecture of certain CPUs. These changes affect the way that ESX Servers perform COW (Copy-on-Write) memory operations when using vSMP in a virtual machine.

There are two common ways to workaround this problem. Perform one of the following workarounds:

  • Instead of rebooting the virtual machine, power-off and then power it back on. By doing this the problem is not noticed because the COW memory is cleared and repopulated upon startup of the virtual machine.
  • Alternatively, you can disable pagesharing which resolves the slow performance. Pagesharing is used to reclaim duplicated memory pages across and within virtual machines. With pagesharing disabled we no longer share memory in this way, therefore the virtual machine consumes more physical memory because all memory pages are duplicated for each virtual machine running on the ESX host.

More info at 


About PiroNet

Didier Pironet is an independent blogger and freelancer with +15 years of IT industry experience. Didier is also a former VMware inc. employee where he specialised in Datacenter and Cloud Infrastructure products as well as Infrastructure, Operations and IT Business Management products. Didier is passionate about technologies and he is found to be a creative and a visionary thinker, expressing with passion and excitement, hopefully inspiring and enrolling people to innovation and change.
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One Response to Slow reboot of vSMP virtual machines on ESX

  1. Steve Anderson says:

    Thank you for posting this, we’ve been poking around for a resolve, I’ve disabled pagesharing on a server that was exhibiting this exact issue, and it appears fixed.

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