Virtual Machine Memory Questions !!

[naveenvm]

1. Can a Virtual Machine power on entirely on .vswp file and memory overhead ? Consider the case of heavy over commitment & no physical memory left. Can the VMkernel swap out the pages to VM's .vswp file and let the VM power on, given the fact it has memory overhead atleast ? Also you have vmx-.vswp file too, so probably it could swap out both overhead and VM's memory to swap files and atleast let the VM power on ?

2. Is there a maximum supported over commitment level for ESXi 5.1 ? like we have for vCPU i.e. 25 vcpu on a core.

[schepp]

1. I'd say the host needs at least the starting amount of RAM + overhead to start the VM as free physical RAM. Haven't tested it though.

Edit:

2. You can find it in the official vSphere configurations maximums. 25 vCPUs per core : http://www.vmware.com/pdf/vsphere5/r51/vsphere-51-configuration-maximums.pdf

[naveenvm]

1. I'd say the host needs at least the starting amount of RAM + overhead to start the VM as free physical RAM. Haven't tested it though.

2. You could calculate a maximum out of the official vSphere configurations maximum doc: http://www.vmware.com/pdf/vsphere5/r51/vsphere-51-configuration-maximums.pdf which would be:

( 512 VMs per host x 64 vCPUs per VM ) / 160 Logical CPU per host = 204,8 vCPUs per logical CPU could be achieved. Sounds scary though

1. Seems Confusing! If you are talking about the minimum RAM required by the guest OS to atleast start ???!!! technically, why can't that be swapped to the swp file as well ?

2. I missed to mention memory! I was asking about the maximum memory over commitment possible ?

Since you have given the formulae for vCPU i.e. the configuration guide itself says only "25 vCPU possible on a core" (and a core may have at most 2 logical cpus)

[JarryG]

I'd say your questions are just hypothetical, but OK.

Q.1: No. VM can not run fully from swap. It needs to have at least some minimal part in real memory. If you already over-commited all your esxi-memory, do not have any free RAM and try to start one more VM, esxi first reclaims some RAM from running VMs.

Q.2: Long before you hit some hard limit for memory-overcommitment your VMs become practically unusable. So even if there is some limit, I doubt you can ever reach it...