Friday, 9 December 2016

Virtualization Oversubscription - What’s so scary? Reservations (11 of 20)

Reservations are associated with Resource Pools or individual VMs.  Essentially you are setting a value for CPU or Memory that the VM is guaranteed to get.  If the VM doesn’t use all its reservation other VMs can make use of the Memory and CPU.

The fairly obvious caveat is that you cannot have a total list of reservations that are bigger than the hardware, this is illustrated below.




VM7 cannot start as the total of VM1, VM2 and VM7 exceeds the 1000 MHz available.

You can use reservations to ensure that important VMs get the resources they want, so you don’t have to worry about avoiding oversubscription for everything.  Pick the VMs you want to perform their best and give them a reservation that ensures that, then your background VMs can be pushed out of the way if required.
Phil Bell
Consultant

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