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Rickard_Anderss
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What do the columns "Host Mem - MB" and "Guest Mem - %" represent?

I can't for the life of me figure out what the columns represent. Here's an example.

I've setup a win2003 server in a virtual machine on one of our ESX servers. The server has been allocated 512 MB memory. Currently, the "Host Mem - MB" column reads 473 and the "Guest Mem - %" reads 27. One would think these numbers mean that the server is using 473 MB of physical memory on the ESX server and that 27% of that 473 MB is actually in use by the guest operating system. However, Task Manager on the server reveals that it is using more like 67% of the available memory.

And by the way, if "Host Mem - MB" is the amount of physical memory used on the ESX server, why isn't it 512 MB exactly?

Cheers,

Rickard

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weinstein5
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Exactly and it has no effect on the guest o/s since it is totaly unaware that it is going on. In regards to which number you should go on really it depends on what are you trying to gauge - if you are concerned that an application inside the guest o/s is not getting enough memory than I would take a look at what task maanger is indicating and if you are concerned with the how memory is being used by VMs - so ot make sure the machines have enough memory allocated you would have to use both values -

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weinstein5
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What you are seeing is the power of Transparent Page Sharing - the vmkernel feature that allows the vmkernel identical memory pages one time in read only memory - the vm needs to write a copy is made and the write occurs - this is completely transparent to the VM's guest O/S - so to the VM's O/S it is using 67% of its memory while ot the vmkernel in the ESX server only 27% is in use -

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Rickard_Anderss
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So, in other words, VMware shares common read only memory pages between virtual machines which means it's using less physical memory on the ESX server than the "sum of the parts"? How does this affect the guest OS? I mean, if a guest OS is using 90% of its memory according to task manager but Virtual Center reports only 50% due to this Transparent Page Sharing, which number should I go bye? I want to make sure that all machines have enough memory allocated and at the same time that they don't have too much allocated.

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weinstein5
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Exactly and it has no effect on the guest o/s since it is totaly unaware that it is going on. In regards to which number you should go on really it depends on what are you trying to gauge - if you are concerned that an application inside the guest o/s is not getting enough memory than I would take a look at what task maanger is indicating and if you are concerned with the how memory is being used by VMs - so ot make sure the machines have enough memory allocated you would have to use both values -

If you find this or any other answer useful please consider awarding points by marking the answer correct or helpful
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Rickard_Anderss
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Ok, thanks. I'm still a bit confused, but things are a bit more clear now.

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