Active Guest Memory vs. What Windows Says is Active

[cbiancotti]

Hi all,

Little background info:

We have one ESX 4.0 server (base, not U1) with about 32GB of physical RAM. Right now I am only running 2 critical virtual machines. One terminal server and an general application server. Terminal server was given ~16GB of RAM, and the app server was given ~8GB of RAM.

Both servers are reporting high memory utilization.

Lets take the application server for example, which doesn't undergo too much utilization.

vCenter reports the following:

Host Memory Consumed: 8.11 GB

Guest Memory Active: 7.68 GB

Yet when I log into the Windows server, task manager reports the following:

Total: 8190 MB

Cached: 832 MB

Free: 1103 MB

So acording to my logic, vCenter should be reporting only just below 7GB actively utilized by the guest? Yet I still get the constant warning/error icons for Virtual Machine Memory usage.

Any input folks? Any help would be greatly apperciated.

PS all the memory resource reservations and limits are set to the default for this server.

[cbiancotti]

Just wanted to bump this. Is this something totally obvious that I'm missing?

[mschwalm]

I've not the solution, but I'm experimenting the same problem on my three ESX servers (4.0). All VMs have between 90 and 95% of memory usage (VM with 512mb, 4Gb,...).

The problem doesn't seem to appear on 3.5 version, so I wonder if it would not be a known problem on 4.0 version. Did you try to install the 4.0 U1 ? I'm going to try it next week, hoping to solve the problem.

Michael

[RParker]

> Total: 8190 MB

First 8190 MB is almost exactly 8GB, not 7.

Second the HOST memory is basically for the ENTIRE VM, not for the OS. ESX has overhead, the VM has overhead, and the OS has overhead, so for a host to allocate RAM requires more memory than what's required, so if you setup 8GB for the VM, and the host takes overhead from the VM, the VM has less than what you intended, so a little more is required to leave the VM with what you expect, so 8Gb from a host is for the VM.

The VM takes some for BIOS (which is same for a physical machine) and the OS sees the remainder of that.

You didn't specify the OS, but I am guessing its Windows 2008, so it uses ALL the RAM and caches the rest until it needs the rest of the RAM, so it shows as active, but not necessarily APPLICATION RAM, so therefore taskmanager is a bit skewed because it's consumed by OS overhead (caching, services, GUI, kernel, etc..), and task manager is showing free for applications, where you get the 1103 FREE.

So the warnings don't take into account shared memory across the VM's (you have only 3 VM's) and as long as your HOST shows memory available and you haven't overcommitted your RAM, you shouldn't worry about the alarms, those are generic, and in time you will get a feel for what ESX needs, and not necessarily concern yourself with thresholds. Alarm is just a counter, and its reporting on the basics.

Your RAM is fine

[cbiancotti]

R Parker,

Thank you for the indepth explanation! That makes perfect sense. Much appreciated!