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VMWare Memory Utilisation

Posted on 2011-05-09
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Physical Host has 16GB RAM

VM1 has 12GB Allocated, Task Manager says 24% being used
VM2 has  6GB Allocated. Task Manager says 30% is being used.

vCentre says the host memory utilisation us 92% and has alarmed on it.

What gives?
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Question by:hongedit
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Andrew Hancock (VMware vExpert / EE MVE^2) earned 2000 total points
ID: 35722550
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ID: 35722561
Well you over comitted the memory of the Virtual Machines beyond what the physical host has!

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by:bgoering
ID: 35722586
I would cut the memory allocated in half on each of your virtual machines. If host memory utilization is that high you have overcommitted memory too much.

Also look and see if you have memory reservations set for those vms. If you do try removing them and letting vmware manage the memory.

How much physical memory is on your ESXi host?
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LVL 124
ID: 35722596
Task Manager in WIndows may report what memory us in use by Windows.

ESX reports what memory has been allocated to the virtual machines.

You've allocated VM1 - 12GB
You've alloocated VM2 - 8GB

Total Allocatd 20GB

Host has 16GB......

Hence why you've got an alarm!

Yes you can over committ memory you don't have, because the phyiscal host will then start to swap to disk, and go slow.
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Author Comment

by:hongedit
ID: 35722679
Well thats the thing.

I have 16GB in the host and 18GB allocated to VM's.

Those VM's arent acutally doing anything right now. One is a dormant Exchange 2010 server with no mailboxes and the other is a McAfee EPO Server.

It seems VMWare memory utilisation reports  on how much is allocated as opposed to how much is actually being used?

I thought you could in theory have a total of say 100GB of RAM allocated but only 24GB in the host. As long as the VM's dont actually use more than 24GB at any one time it should be ok?
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LVL 124
ID: 35722693
That is correct.

That is also correct.

Yes, all your assumptions are correct.
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Author Comment

by:hongedit
ID: 35722728
Well looking at "Active" memory un Resource Allocation for each VM:

VM1: 122MB
VM2: 614MB

So in reality only 766MB is being used.

But vCentre still complains that nearly all is used.

Correct?
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LVL 124
ID: 35722737
Yes, because you've allocated it, to the VM from the main memory pool on the ESX server.

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LVL 124
ID: 35722745
So because the VMs could use 12GB and 6GB, that memory has been allocated from the pool for them.
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LVL 124
ID: 35722749
if you've allocated too much, reduce it on the VM, and in the future, if you see, the VM is using it, and nearing 100%, increase the memory allocated to the VM.
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by:hongedit
ID: 35722780
Just something I'll have to get used to I guess.

Say I moved the other 2 VM's over, (which are similar memory useage to the 2 we are talking about), it should be easily handled.

But VMWare will probably self-implode :D
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LVL 124
ID: 35722792
No, it will not.

You will severly over commit the memory in the server, it will start swapping to disk, and performance will be poor.
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Author Comment

by:hongedit
ID: 35722805
Why would it start swapping though if actual memory usage is low?

I thought VMWare was intelligent enough to realise this?
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LVL 124
ID: 35722830
here's another guide to have a read of when time permits

http://www.vmware.com/files/pdf/perf-vsphere-memory_management.pdf
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