Resource Question

[prutter]

I'm battling back and fourth with my manager about resources needed for servers and i need somethign clarified. vCenter shows that the servers active guest memory is using roughly 800MB (15% of total) but the server shows it's utilizing 2.5GB (50%). CapacityIQ shows it as under utilized as well. This guy wants me to throw more memory at it but i won't. Can anyone tell me the difference between teh two readings? Any help is appreciated. Thanks.

P

[RParker · Accepted solution]

First of all the OS is correct. Whatever the OS shows INSIDE the VM (which includes vCenter OS) THAT's the ONLY thing you should be concerned about.

If VMA running Windows 2008 server has 4GB assigned, and active memory is showing 800 meg, yet The ESX HOST shows 2.5GB used, that has ZERO, NOTHING, NADA to do with HOW the OS is actually USING this memory. It just means the esx HOST has to allocate RAM in the amount of 2.5GB to give the VIRTUAL machine what it wants to run, but the OS INSIDE manages the RAM given, not the host.

So those numbers from a ESX perspective may be a bit high, but the OS and vCenter OS are the ONLY ones that matter. If they have 4GB of RAM, and they are using ONLY 800Meg.. that means 3.2 (roughly) is FREE, you can double the RAM, it ONLY means it will have MORE FREE RAM, it's not going to use more RAM.

So tell your manager, he doesn't know everything, he needs to let you do your job and leave SYSTEMS to the experts. He needs to be less micro management.

[RParker]

Another interesting side note, you can give the VM the RAM. Now use the slider under resources and move it to half (so if you had 4GB, and you configure it for 8GB, moving the slider half way means you are limiting the RAM to what you set originally).

You can do this WHILE the OS is running.. and PROVE your point. That constricting the RAM reduces FREE RAM, not the RAM it's using, and this is further proven by watching the swap file. if the SWAP file DOES NOT increase, then obviously it's not starving for memory.

[prutter]

THanks for teh reply. The way i understood it was that if i giver teh vm OS 4GB of RAM (Exchagne server) certain processes will take so much of that eve though it doesn't need it. So it shows 50% of the total used up. In Vcenter it only shows 15% and that is the actual amount that the OS is using in reality. IS this correct??