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danarstevenson
Contributor
Contributor

Clarification Needed please

Good morning,

I would like clarification on what < ESX 4.1 > under the Sumary tab > Resources the Memory Usage really stands for please.

memory.jpg

Does that represent the used memory on the server based on all of the VM's running or what is it.

Here is a list of the servers on the machine at the time of the screen shot

vms.jpg

Any help to clarify my confusion would be great.  I keep getting alerts of ussage in vCenter so just making sure I understand what is going on.

Thank you very much

Dana

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RParker
Immortal
Immortal

You are confusing usage vs what is allocated.

Your host allocates memory to VM's based upon their need.  Memory is assigned (and therefore reserved) to VM.  Your host represents this memory as being allocated to VM.

Those VM may not be using ACTIVE memory, but OS like Redhat 6 and Windows 2008 R2 will use that memory for cache.. so it doesn't show up as used RAM but it IS being used by cache.  When the OS needs more RAM, it will reduce the cache..

Right now that memory is in use.. all of it, that's why the host shows high usage.

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danarstevenson
Contributor
Contributor

Is there a way to confirm the usage on the guests at all,  I understand your statement and have no issues understanding what you are saying.  But ,  is there a way to show two reference points to show the memory usage results? 

If I add up the memory ussage in each guest this may result in the same usage report.

Just wondering. 

Thank you for the information

Dana

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RParker
Immortal
Immortal

danarstevenson wrote:

If I add up the memory ussage in each guest this may result in the same usage report.

Actually it won't, there are 3 different metrics.  There is guest OS and what it THINKS it has.  There is Transparent memory sharing that is being shared between VM's (that cannot be measured) and then there is the ESX host that is allocating memory to each of the guests.

You can login to each VM, see usage from task manager or similar tool, but it will not coincide or match what VM ware sees.  There will be variations, because a guest OS may have 4GB accessible, VM thinks it's using 512 Meg active, but in reality the cache isn't ACTIVE memory it's dirty memory, and that memory can be used for another purpose, so you will not get this information.. maybe perf mon CAN let you monitor this but it will still not let you see correlation between ESX host and guest OS.

For that you need a tool like Foglight or Veeam report server.. they can let you drill down from ESX all the way to the guest..

But the bottom line is the memory is being used, it's just how you look at it.  VM tools (which is where the active memory, consumed, granted) shows what is going on inside the guest, but it's not 100% accurate, it's only from 1 app perspective...

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