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RESXTOP Memory Counters for Host Memory Swapping June 17, 2012

Posted by vbry21 in RESXTOP.
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I mentioned in an earlier article that within a VMware ESXi environment that Host Swapping was a bad thing, the reason for that is, if an ESXi host runs low on physical RAM, then the issue is, that VMs memory will be swapped to disk. This host level swapping severely affects the performance of the VMs being swapped.

Based on the above statement, we should monitor for swapping.

We could check the advanced performance graphs in our vSphere client, what we would do is highlight our ESXi host, click on the Performance Tab and then select Memory from the drop down, we are interested in two counters.

Memory Swap In Rate – The rate at which memory is swapped from disk.

Memory Swap Out Rate – The rate at which memory is swapped out to disk.

We can also use RESXTOP from the vMA virtual appliance, the most interesting counters are listed below.

From RESXTOP press m to access the memory counters.

SWR/s – This indicates the amount of memory, measured in megabytes and represents the rate at which the ESXi host is swapping memory in from disk.

SWW/s – This indicates the amount of memory, measured in megabytes and represents the rate at which the ESXi host is swapping memory to disk.

SWCUR – This is the amount of swap space currently used by the virtual machine.

SWTGT – This is the amount of swap space that the host expects the virtual machine to use.

Just as an additional bit of info, we can also get some useful statistics from the CPU screen (press c within the RESXTOP screen).

%SWPWT – This gives us an indicator of a performance issue due to wait time experienced by the VM. It represents the percentage of time that the VM is waiting for memory to be swapped in.

 

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