inquiry about CPU reservation settings

[RUG201110141]

I've got a silly question that I guess I would like some clarification or confirmation on. I don't use reservations much in our present environment but we are starting to virtualize some SAP systems. SAP recommends to use reservations for SAP virtualized machines. Reserve all resources (cpu & memory) for the virtaul machine so that if there are contention issues on the host the virtual machine is guaranteed to get the resources it needs. I got that part and it makes sense. So if I have a cluster of ESX servers that are identical and they have 2.931GHz processors in them and I have a virtual machine that is a 2vCPU to create the appropriate reservation for the virtual machine I just go 2x2.931GHz for a reservation of 5862MHz.

Is that accurate reasoning for setting CPU reservations for a SMP virtual machine?

[weinstein5 · Accepted solution]

That is correct - you have reserved to cores worth of CPU cycles - also keep in mind a VM will not start if its resrvation can not be satisfied so if you start adding other VMs with reservations and powering them on you can come to point where you will not be able to power on additional VMs

If you find this or any other answer useful please consider awarding points by marking the answer correct or helpful

[Rajeev_S]

Also, CPU cycles reserved cannot be used by the other VM's in the cluster. eventhough your SAP server is not using the reserved cycles.

Ensure you do size the reservations properly.

Hope this helps.

[Rajeev_S]

Also, cpu cycles reserved cannot be used by the other VM's in the cluster, eventough your SAP VM is not using it.

Ensure that you size the reservation carefully.

Hope this helps

[depping]

Keep in mind that when setting a reservation you are dictating the slot sizes that HA uses to calculate the amount of available slots for an HA cluster. This could thus lead to a very conservative amount of slots which might not be desired.

Duncan

VMware Communities User Moderator | VCP | VCDX

-

---

Now available: vSphere 4.0 Quick Start Guide: Shortcuts down the path of Virtualization

Blogging: | Twitter: