How low can I set my memory limit?

[Brian69]

I've read a bit about setting the reserve and limit values of memory and CPU for VMs and I understand what they do. What I'm not really sure on is what the numbers mean in the last three columns of my attached image vmperf1.jpg or vmperf2.jpg. Unless I really don't know what I'm talking about, "Guest Mem %" seems to indicate that the VM is using this percentage of the memory it has been allocated by ESX. If that's the case, and the VM is not a highly used or highly trafficked machine, could I theoretically set my memory limit fairly low to regain some resources? Help me understand these numbers. If you have links so I can RTFM, that would be excellent.

[KevinMC · Accepted solution]

Here is a link to the resource management guide for 3.5. Hope it helps. I would make sure to take a look at the server memory usage over time (week/month) before setting your limits too low as server memory consumption can vary greatly based upon the load.

Kevin

[kjb007]

Limits will cap the amount of memory your vm can use. Instead of a limit, adjust the amount of memory allocated instead. Why would you want to allocate x number of MB to a vm only to limit the vm to only half that amount?

See my post here: http://communities.vmware.com/message/1383972#1383972 regarding the numbers you asked about.

-KjB

VMware vExpert

Don't forget to leave points for helpful/correct posts.

[MattG]

Using memory limits allows you to "dynamically" add physical memory to a running VM. For example, I could assign a VM 2GB and limit it to 1GB. If in the future I wanted to "hot add" memory I could remove the limit on the VM and it would use 2GB without reboot.

That being said, the recommendation is to not modify the default settings unless you have a specific requirement.

-MattG

If you find this information useful, please award points for "correct" or "helpful".

[kjb007]

So, do you by default allocate 2+ GB to every vm in order to provide this "feature"?

-KjB

VMware vExpert

Don't forget to leave points for helpful/correct posts.

[MattG]

Absolutely not. I stick with defaults unless I have a specific requirement to control the memory beyond the defaults.

-MattG

If you find this information useful, please award points for "correct" or "helpful".

[Brian69]

Ok... that post helps. Let me post another snapshot and ask you to tell me specifically what the numbers mean. There's only one column on the "Virtual Machines" tab for CPU usage which is simple enough to understand. It's the need for 3 memory columns that has me confused. Can you explain the numbers in the attached screenshot?

Message was edited by: Brian69

Kevin, thanks for the reference link. I'm reading it now.

[K-MaC]

Hello Brian,

Please see the following post for information on memory usuage.

http://communities.vmware.com/thread/52352

Cheers

Kevin

[java_cat33]

The host memory column is the amount of host memory being used by each VM.

The guest memory % is what vCenter thinks the amount of VM usage is on the guest - this percentage is calculated from a number of samples taken of a certain time period.

The memory size column is the amount of allocated memory to each VM.

As mentioned by a previous poster - I definitely wouldn't set a limit on your VM's unless you've got some strong reason for it. Setting a limit will cause the VM to start ballooning (if the memory limit is breached) - making the OS swap, and then eventually it may start swapping to it's VM swap file in a worst case scenario if the VM is trying to use more memory than what it's limit is set to.

[Brian69]

This thread was pretty helpful. Thanks for the good info. I ended up reading more of the resource guide than I actually had time for.