Memory Overcommit?

[csyckad]

Sorry, I am new to vmware,  I read some vmware document,

But I want to know the memory resource control?

If the memory overcommit, the esx will do page sharing, balloon and finally swapping.

But the memory overcommit mean all vm guest assigned memory ? vm guest active using memory?

Our VDI host have 150GB physical ram(VM assigned around 260GB ram), The physical memory usage is around 80%,

but we saw many page share and balloon in the performance tab, 

I think is not enough memory so incur balloon and swap to make the vm guest performance poor.

But my boss think "Memory overcommit" is mean sum of all vm guest active memory.

we didnt set the memory reserve.

I am going to propose, set each vm guest ram (win 7 64 bit) and reserve 2Gb ram.

Currently most of them set 8GB ram but didnt setup any reserve, in the vm guest usage, i dont see many memory usage, so i think reduce the each vm memory and do the reserve will make all performance is better

[admin]

Hello,

Consumed Host Memory usage is defined as the amount of host memory that is allocated to the virtual machine and Active Guest  Memory is defined as the amount of guest memory that is currently being used by the guest operating system and its applications.

The concept of memory over commitment is fairly simple: host memory is over committed when the total amount

of guest physical memory of the running virtual machines is larger than the amount of actual host memory.

Your Boss is correct Memory over commit is sum of all VM guest memory greater than the Host actual memory that is available for usage.

You find as a  difference because

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

Hope this was helpful.

Thanks,

Avinash

[csyckad]

Sorry about "

The concept of memory over commitment is fairly simple: host memory is over committed when the total amount

of guest physical memory of the running virtual machines is larger than the amount of actual host memory."

From the understanding, for example, the host have 4GB ram, now i have 2 vms, each VM have assigned 1vCpu and 3 vRam, even their usage is low, Is this overcommitment ? Or each VMs active memory?

Or any official doc to mention it?

Thanks

[admin]

HI.. check this the official doc on the same.. https://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.vsphere.resmgmt.doc%2FGUID-895D25BA... also  sending a video link to more clarify. http://www.youtube.com/watch?v=Abot9mAHqNo i hope it will help you.. Thanks

[abhilashhb]

Yes if you have 4GB RAM and you create 2VM's with 3GB RAM its called over commitment. Its the memory assigned not the VM's active memory. Even when you over commit make sure there is enough memory on the physical host. Ballooning and TPS are ok to a level. If a contention takes place to a level where its swapping from disk it will ruin the performance(unless you have SSD)

Its good that you are thinking of Setting reservation. If you set reservation it will assure the VM's that they will get that amount of RAM what ever happens.

And what your boss thinks is wrong. Its not the sum of active memory usage but rather the Memory assigned to all the VM's.

If you have 4GB RAM and host. There are 3 VM's each with 2GB its over-commit. But their active usage might be just 3GB. or their usage might go to more that 4GB. That's when memory techniques will come into picture.

[Gabrie1]

Maybe these two posts can help you (even though a bit old):

Memory overcommit in production? YES YES YES

and

http://www.gabesvirtualworld.com/memory-management-and-compression-in-vsphere-4-1/