I have ESXi 5.1 running on 2 hosts with less than 10 virtual machines between them currently.

Host 1 has 12GB RAM (Resource Allocation tab says 9288MB)

Host 2 has 16GB RAM (Resource Allocation tab says 13203MB)

I'm still not clear why I lose 3GB of RAM per host (the Memory Usage: Capacity figure on the Summary Tab shows the full amount) but that's sort of another issue (feel free to enlighten me though).

My question is: I've bought an Essentials licence and that gives me vCenter server. I'm deployed the virtual applicance for this (on Host 2) which comes configured with a memory size of 8GB. Sure enough under the Virtual Machines tab for that host it quickly shows Host Memory of around 7500MB however the Guest Memory percentage often falls to a low figure), e.g. less than 10.

This implies that the memory is allocated on the host but isn't begin used by the guest. I think I read something that says once ESXi has allocated the memory it won't actually release it.

Given how small my installation is (in relative terms) would I benefit by going into the settings for the appliance and reducing the memory down from 8GB to 4GB (or even less). Or is this totally irrelevant as will ESXi simply move that 7500MB onto disc and reallocate the actual RAM should another Guest need it?

I hope that makes sense. Thanks for your help.

2 Answers 2


No, you don't want to potentially memory-starve your VC, buy more memory, it's cheap and your hosts are criminally underspec'ed.


Lowering it should be alright for your usage. Vmware recommends a minimum of 4GB memory for a server controlling under 10 hosts

  • For a lab or home setup, sure, but that's not what ServerFault is for. For a business/production network he barley has enough RAM as it stands. Commented Nov 16, 2017 at 16:27

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