13erla
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Enthusiast

hitting 100% memory impact

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on esx 302.

if a host does hit 100% memory usage. what is the expected impact to the Host and the vms running on it?

say the host has 32gb of memory. would the VMs just start paging? some crash? small performance hit depending on how much over the 100%?

if they are paging, will they page to the page file on the SAN? (vms in this scenario would be all san attached) or would they page within the guest OS?

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Morten_Dalgaard
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When the host is running low on memory it will attempt to use the ballooning driver in the guest vm's (installed via vmware tools), to force the guest vm's to release memory back to the host.

If the ballooning driver is unavailable (no vmware tools installed), or the ballooning driver is unable to grow any larger, the host will start paging the vm's to the swap file created in the vm's folder when a vm is started (meaning on the SAN).

vmware will use a combination of the two methods above, but prefer the first one.

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Morten_Dalgaard
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Enthusiast

When the host is running low on memory it will attempt to use the ballooning driver in the guest vm's (installed via vmware tools), to force the guest vm's to release memory back to the host.

If the ballooning driver is unavailable (no vmware tools installed), or the ballooning driver is unable to grow any larger, the host will start paging the vm's to the swap file created in the vm's folder when a vm is started (meaning on the SAN).

vmware will use a combination of the two methods above, but prefer the first one.

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Rodos
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Have a quick skim of the whitepaper The Role of Memory in VMware ESX Server 3. It provides some great details.

It discusses such things as how shares effect memory, the memory tax, memory sharing and how ESX dynamically expands or contracts the memory for a VM.

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