Memory overhead in my vm?

[Dhakshinamoorth]

Hi all,

I have one vmware ESXi 4.1 server (build 260247) on HP DL120 Server with the configuration of 10 GB Ram,Intel Xeon Quad core processor,500 GB Local SCSI HDD.I installed one Guest 2003 operating system as 6 GB Ram,2 vCPU,150 GB HDD-Thin format. I can see the "Memory overhead" =171.17 MB.

what is memory overhead? "memory overhead" and "memory overcommit" is same concept or not? any calculations for memory overhead? how can i prevent this? suggest me please.

[dougdavis22]

Memory overhead is the RAM used by the ESX host itself to run the virtual machine.  This doesn't affect the memory allocated to your virtual machine, but you need to take it into consideration as it is taken out of the total RAM installed in the host.  So, if your VM has 6GB RAM allocated, it will actually consume 6GB + the memory overhead from the 10GB installed in your host.

Hope this helps.

Doug.

[VTsukanov]

Memory overhead

Each VM running on an vSphere consumes some memory overhead additional to the current usage of its configured memory. This extra memory is needed by ESX for the internal datastructures.

Memory overcommit

Your virtual machines can use more memory than the physical machine (the host) has available. For example, you can have a host with 20GB memory and run four virtual machines with 6GB memory each. In that case, the memory is overcommitted (I worked with the ratio 1 / 1,2; phys / summ virtual)

Overcommitment is an especially effective technique for maximizing memory use because, typically, some virtual machines are lightly loaded while others are more heavily loaded, and relative activity levels vary over time.

Take a look Understanding Memory Resource Management  in VMware® ESX™ Server

[shishir08]

Every 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 by ESX for the internal VMkernel datastructures like virtual machine frame buffer and mapping table for memory translation (mapping physical virtual machine memory to machine memory).These are memory overhead.

Memory overcommit (or overcommitment) is a hypervisor feature that allows a virtual machine (VM) to use more memory space than the physical host has available. Memory overcommit is the combination of three key ingredients:

    Transparent memory page sharing
    Balloon driver
    Optimized algorithms in the hypervisor kernel
    These 3 elements must all be present and work together seamlessly.

Memory overcommit enables  to achieve higher VM density per virtual host, increasing consolidation ratios and providing a more efficient scale up - scale out model. Ultimately this translates into substantial savings and a lower cost per application than with alternative solutions

[UmeshAhuja]

Hi,

VM’s host memory usage <= VM’s guest memory size + VM’s overhead memory

Here, the virtual machine’s overhead memory is the extra host memory needed by the hypervisor for various virtualization data structures besides the memory allocated to the virtual machine. Its size depends on the number of virtual CPUs and the configured virtual machine memory size.

For more information, go for vSphere Resource Management Guide

[UmeshAhuja]

Hey ,

I found one PDF regarding memory resources management with 4.1 vmware. Its too good and helpful.

http://www.vmware.com/files/pdf/techpaper/vsp_41_perf_memory_mgmt.pdf

[nava_thulasi39]

Hi,

Additionally memory overhead calculated based on number of vCPU & RAM.

From the resource managment guide