Virtualization Oversubscription - What’s so scary? (17 of 20) Expandable Reservation

When a VM starts the Reservation set for that VM is taken from the Reservation available within the Resource Pool.  The total reservations of the child VMs may not be more than the Reservation for the Resource Pool.

However if Expandable Reservation is turned on then a Resource Pool may satisfy its Reservation requirements by using the Reservation of another Resource Pool.  This however may stop the 2^nd Resource Pool from starting VMs as it itself cannot satisfy the Reservation requirements of the VM which wants to start.

When a VM starts the Reservation set for that VM is taken from the Reservation available within the Resource Pool.  The total reservations of the child VMs may not be more than the Reservation for the Resource Pool.

I'm off on vacation now and will be back in the New Year to deal with ' What's the worst that can happen?'

Wishing you all a Happy Holidays and see you in 2017!

Phil Bell

Consultant

Virtualization Oversubscription - What’s so scary? Reservations, Shares and Limits (15 of 20)

Reservations, Shares and Limits apply to the amount of CPU and Memory a VM or Resource pool can use.
In the example below we have an Engineering Resource Pool containing 2 Virtual Machines.

Test has 1000  CPU shares and Production has 2000 CPU shares, giving a total of 3000 shares between them.  If there is contention for CPU resource then Production will be given twice as much CPU time as Test.

Also notice the reservation on the Resource Pool has an Expandable Reservation.  This means that if there is another resource pool not using its reservation Engineering could claim and use that reservation if required.  This could cause problems if the 2^nd resource pool wishes to use its reservation as it will not be able to push Engineering out.  So while this may provide flexibility its use should be closely monitored.

On Wednesday I'll give a quick demonstration of what a reservation does.

Phil Bell

Consultant