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RESXTOP memory counters for the Ballooning mechanism June 18, 2012

Posted by vbry21 in RESXTOP.
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Balloon Driver Counters in RESXTOP

In a previous post I mentioned that the balloon driver wasn’t necessarily a bad thing, the reasoning behind this is as follows.

Ballooning as a process is part of normal operations when your host memory becomes overcommitted, now think of your normal physical servers, if you have a server with let’s say 8 GB of RAM, would you expect that server to be constantly using 8GB of RAM, hopefully the answer is NO!!!

The fact that the ballooning is occurring does not necessarily indicate a performance problem, if we also get swapping, then we do have a problem.

What the balloon driver does is allow the guest VM to give up physical memory pages that are not being used. To enable this all we have to do is install VMTools.

Onto the counters that are useful metrics to analyse, these are important in that, even though ballooning is not a bad thing, the counters give us an indication that perhaps we are approaching memory saturation.

To access the counters hit m when in RESXTOP to access memory

MEMCTL/MB – This line will display the memory balloon statistics for the entire host. All numbers are in megabytes.

The ‘curr’ is the total amount of physical memory reclaimed using the ballooning mechanism.

The ‘target’ is the total amount of physical memory ESXi wants to reclaim with ballooning.

The ‘max’ is the maximum amount of physical memory that ESXi can reclaim with ballooning.

MCTL?- This value is either Y for the balloon driver installed per VM and N if not installed.

MCTLSZ – This value is also reported per VM and represents the amount of physical memory the balloon driver is holding for use by other VMs.

MCTLTGT – This value is also reported per VM and represents the amount of physical memory that the host wants to reclaim from the VM.

MCTLMAX – This value is also reported per VM and represents the amount of physical memory that can be reclaimed as a maximum.

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