grahamhyland
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Contributor

Memory Sharing Question

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Hello,

I hope someone could help me, I am wondering what is the best was to give memory to VM's we have a server with 16GB ram If I give 2GB to the Vms i only get 8 machines.

The question is , Is this bad practice? should i give each VM something like 256MB and let them baloon for more?

Does balooning need to be configured or does it just happen. VI3

Thanks

Graham

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jrenton
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The balloon driver will only kick in when the host is running low on memory. This will only happen if you have assigned more memory to virtual machines than is available on the host. A virtual machine will not be able to access more memory than is assign eg your 256Mb.

Best practise is to only assign available memory in the host and buy more hosts when you run out of resources in your cluster. The balloon driver is there as a last resort, eg. if a host fails and VMs from this host are moved onto other hosts thus using up all available memory in those hosts.

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jrenton
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The balloon driver will only kick in when the host is running low on memory. This will only happen if you have assigned more memory to virtual machines than is available on the host. A virtual machine will not be able to access more memory than is assign eg your 256Mb.

Best practise is to only assign available memory in the host and buy more hosts when you run out of resources in your cluster. The balloon driver is there as a last resort, eg. if a host fails and VMs from this host are moved onto other hosts thus using up all available memory in those hosts.

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jrenton
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Assign memory to each virtual machine as required. A DC will probably not need 2GB of memory but a SQL server probably will.

This doc may be helpful:

weinstein5
Immortal
Immortal

Keep in mind when you set memory on a VM it is the amount of memory which the guest O/S will be told it has access to - this means if you set your VM memory to 2 GB and the O/S is only using 512 MB that is the amount of memory it will get access to - another thing ESX utilizes Transparent Page Sharing - the ability to recognize identical pages being stored by the VM and store them only one time - when the vm goes to write that page acopy is made and the write occurs to that page - the balloon mechanism does not provide additional memory to the vm but allows the vmkernel to influence how and win the vm's O/S utilizes its own virtual memory - so in your example if you set the memory to 256 MB that is all the memory your VM will get - to get ballooning you will need to install VMware Tools in the VM -

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