Comments on: Virtual Machine memory overhead

By: Rafał Mróz

Rafał Mróz — Fri, 20 May 2011 16:14:09 +0000

Been a year, but still the info is usefull. Anyway the link to the site doesn’t even come close to make proper sizing. Backing it with own example:

RP with 1 VM: 1 vCPU and 1024MB running Win7 32bit
Using the table I’d need at least 123,73MB of reservation on RP (if it’s the static you mention). I’m able to poweron VM when I have at least 181MB reservation though. Minute or two after VM poweron the resource allocation tab shows overhead consumption at 104MB and overhead reservation at 161MB. So there’s no way to match any of the numbers.

The differences rise when we switch from Win7 32bit to RHEL6 32bit – I’m not able to poweron the VM at 181MB, but after I do (expandable, don’t want to search for single number) the resource tab shows 42MB of consumption and 101MB overhead reservation.

Haven’t check the VMware site yet to find any other table, but this table is of no use to do proper minimal sizing. Any info on that?

By: Vertial memory | CftcStx

Vertial memory | CftcStx — Sun, 06 Mar 2011 23:10:54 +0000

[...] Virtual Machine memory overhead | frankdenneman.nlEvery virtual machine running on an ESX host consumes some memory overhead additional to the current usage of its configured memory. This extra space is needed … Resource pool memory reservations; This means that during the design phase of a resource pool, the memory overhead of a virtual machine must be included in… [...]

By: Technology Short Takes #1 - blog.scottlowe.org - The weblog of an IT pro specializing in virtualization, storage, and servers

Wed, 18 Aug 2010 05:37:23 +0000

[...] was published almost three months ago. Still, one phrase in this article by Frank Denneman on VM memory overhead really caught my eye: Please be aware of the fact that memory overheads are growing with each new [...]

By: Frank Denneman

Frank Denneman — Tue, 01 Jun 2010 19:07:12 +0000

Nitro, Michael dynamic overhead totally depends on the workload and can change while the virtual machine is running.
Shadow page tables play an important role in sizing the dynamic overhead as it can shrink and grow according to the virtual machine guest os workload. When the VMM wants to add more shadow page tables, it will request an increase in the amount of overhead memory.

Michael, yes the memory overhead is different, but whats even more suprising is that VMware stopped mentioning the virtual machine guest OS. Im not sure if it doesn’t have impact anymore on the size of the overhead or that just listed the worst-case scenario

By: michael

michael — Tue, 01 Jun 2010 06:49:32 +0000

Thanks for the info.
What dynamic overhead memory is used for?

I remember that in ESX 3 memory overhead was different for 32 and 64 bit VMs. Has this been changed in vSphere?

By: NiTRo

NiTRo — Mon, 31 May 2010 19:05:36 +0000

Very interesting ! Any numbers to put in front of Dynamic overhead ?