Resource utilization query

[kartheekmunaga]

I have created a vm(xp 32 bit) on top of a standalone esxi host.

Config of XP vm

1 vcpu

516 MB ram

reservation 212 MB

limit 512 MB

overhead reservation is 50 MB

The question is the vm is using more host memory according to the screen shot attached file

guest mem+overhead mem(180+50)= 230 MB which is not equal to the host memory 479 MB, where did the remaining host mem is utilized(479-230=249 MB)?

[Virtualinfra]

1. Host Memory is the amount of physical memory that has been allocated to a virtual machine
2. Guest memory is the memory usage of a virtual machine.

as per the screen shot ESX host is provided  479 MB of physical memory out of 512 MB which can be used by virtual machine instantly. and Virtual machine requires only 180MB of memory to process its operation which is shown in guest memory tab..

If guest memory show above 500 and host memory show 479.. that means 479 MB physical memory is used and remain is swaped.

Hope this clarifies..

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[rickardnobel]

Dharshan wrote:

1. Host Memory is the amount of physical memory that has been allocated to a virtual machine
2. Guest memory is the memory usage of a virtual machine.

The guest memory in this view is the "active" memory, which is really not the memory usage of the virtual machine, but a estimate on how much amount of the consumed memory that have been recently been accessed inside the VM. The virtual machine might have loaded data in much larger areas of memory than 180 MB in this case, but only about 180 MB have been read or written during a sample interval.

[Virtualinfra · Accepted solution]

Rickard Nobel wrote:

Dharshan wrote:

1. Guest memory is the memory usage of a virtual machine.

The guest memory in this view is the "active" memory, which is really not the memory usage of the virtual machine, but a estimate on how much amount of the consumed memory that have been recently been accessed inside the VM. The virtual machine might have loaded data in much larger areas of memory than 180 MB in this case, but only about 180 MB have been read or written during a sample interval.

What does "but a estimate on how much amount of the consumed memory that have been recently been accessed inside the VM." this mean, different from the memory usage of a virtual machine.- yes offcourse the memory is not constantly utilized in any server so there will a value change in frequent of time. even when we notice in task manager.

Cosumed memory that have been recently been accesed inside the VM, refers the memory used by the virtual machine.

For further clarification:-

Consumed memory is nothing but the physical memory allocated to the VM and guest memory is nothing but the active memory used by the Virtual machine out of the consumed memory(physical memory) in this case the consumed memory is 479MB and guest memory(active) is 180 MB. Yes the values are up and down, because the memory usage is not constant in server..so the value will be getting periodically changed or updated frequently.

Please refer the below screen shot of my virtual machine is very much same inside and out side the VM..here the physical memory is 700 and active memory is 1003.

[rickardnobel]

Dharshan wrote:

What does "but a estimate on how much amount of the consumed memory that have been recently been accessed inside the VM." this mean, different from the memory usage of a virtual machine.- yes offcourse the memory is not constantly utilized in any server so there will a value change in frequent of time. even when we notice in task manager.

There is actually a large difference. The "active" memory is not how much memory the virtual machine is using, but just a sample on how many pages that has recently been touched.

The amount of memory being used by the virtual machine could be much greater. This means that inside the VM much more data is often loaded into guest memory than being reported by "active" outside.

[kartheekmunaga]

Can you please tell me about overhead reservation is 50 MB in the above case.

My guess its extra memory for vm(not config memory to the vm)  to power on and its using extra physical host memory.

this overhead reservation is included in the consumed memory(host memory)?

[kartheekmunaga]

I undersatnd what you have said, but what is the use of dispalying the information about how many pages that has recently been touched rather it will much helpfull if shows the actual memory usage of the vm.

[rickardnobel]

kartheekmunaga wrote:

but what is the use of displaying the information about how many pages that has recently been touched rather it will much helpfull if shows the actual memory usage of the vm.

Yes, that is often not interesting to see the recently touched memory. (It could be in some resource planning.) If you instead see the "Consumed" then this will show you how much physical memory your Virtual Machine actually is using. This could be seen as the "memory cost" of the VM.

See this example below, a Windows 2003 VM which internally uses over 800 MB:

And in the vSphere Client:

As seen the active memory is very low, this means that about 81 MB has been recently touched inside the VM. On the "Consumed" tab we can see that the Transparent Page Sharing feature has collapsed some similar pages and saved physical memory, so the whole VM uses 622 MB.

The Overhead as you asked is memory that the VMkernel uses outside of the VM for different purposes, it is an additional cost per VM. It will depend on the number of vCPU and vRAM given to the VM, if more of these then larger memory overhead.