VMware

VM Memory

Hey, one of my VM Administrators posited that when you give a VM a non-power-of-2 (in thase case 3 ) GB of memory, VMWare actually reserves up to the next power of 2 (in this case 4) GB of memory.

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Is that true?


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3 Comments

  1. That’s not true, assuming you’re speaking about ESXi. RAM isn’t even reserved unless a VM is actively using all of the assigned RAM or if you enable hard reservations.

    What unusual RAM amounts can do is make it somewhat difficult to efficiently balance multiple VMs to work optimally with regards to NUMA boundaries. This just sounds like someone who’s ill informed or is making up excuses to stick to with company standards.

  2. If that were true it would be well documented and well complained about.

    memory was usually deployed in powers of 2 because ram sticks were usually base2. You also deployed ram in two sticks because of dual channel memory performance improvements.

    That being said, I believe it will round up to the next base2 number, so if you were to put in some number that’s a decimal between 0.0 and 1.0 but you’re talking about rounding up a fraction of a KB to the next whole KB number.

    I still get people complaining when they see all of my odd-numbered vcpu and vmem assignments, but their argument is both “Never seen that before” and “isn’t that wrong?” It’s 2020, virtualization has been around for over a decade.

  3. That is not the case at all.

    In fact in Vmware virtualization, it works on demand not by allocation. So even if you give 4 GB RAM, it won’t consume that unless there is demand for it. Most of the time it will never touch the allocaition.

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