Problem Why is my Hyper-V Cluster showing as overcommitted?

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I'm trying to determine why my Hyper-V cluster is saying I will be overcommitted with the creation of my next VM. I'm unclear whether its the CPU or the RAM, so I'll give a breakdown of both.

The cluster has two host nodes, each with 24 GB of RAM and 2 Quad Core Procs. Host reserves are all on the defaults. So 512 MB of RAM is reserved for the hosts and 20 percent CPU. My understanding, at least RAM wise, is this give me roughly 23.5 GB of usable RAM in the cluster to work with before its status goes to over committed (that's after subtracting the 512 MB of host reserve).

Here are the current VM configurations in the cluster:

VM1: CPU = 4 and RAM = 4 GB
VM2: CPU = 4 and RAM = 4 GB
VM3: CPU = 4 and RAM = 4 GB
VM4: CPU = 4 and RAM = 4 GB
VM5: CPU = 1 and RAM = 1 GB
VM6: CPU = 1 and RAM = 1 GB
VM7: CPU = 1 and RAM = 1 GB

That puts my total RAM usage at 19 GB, leaving me with 4.5 GB to play with.

The current status of the cluster is "OK", but if I try to create a new VM now, regardless of how much RAM I specify (I've tried 512 MB and even less), I get no stars in my host ratings and the rating explanation is:

"This configuration causes the host cluster to become overcommitted"

I've verified that the "Cluster Reserve (nodes)" is set to 1.

Can anyone shed some light on what might be the possible cause of this?

 

Yeah I had seen that one before but after searching google for awhile I found a Technet Post that disagrees with that calculation. Also when going over this calculation for our environment, we should be already overcommitted according to this which we are not at the moment. It's when we try to create a new VM that it shows that we will be overcommitted.

Also just thinking about that calculation, say for example that we have a SQL server with 16GB of RAM. Would that mean that each VM would technically be calculated with 16GB, meaning that we would have to have 128GB of memory in each host to accommodate the 8 VM's in which one of those has 16GB's. That just seems crazy, you know what I mean?

This is really confusing me and puts us in a tough place, I know we are going to need more memory (have order another 24GB's) but we should be able to create another 1-2 VM's with the 4GB of unused space that we should have.

Any other thoughts?

 

It's all good, it's an interesting thing. Been testing a lot today trying to figure out how it all works. I found a post about how SCVMM calculates whether or not your overcommitted but it doesnt make sense how he explained it, here is the link if anyone can figure it out:

http://social.technet.microsoft.com...v/thread/0e571138-1704-4458-9744-3916e2c0ef64

It's Mike Brigg's answer that he tries to explain how to calculate it but it doesnt make any sense.

Thanks for your help Ken, if anyone else has experienced this please chime in.