Agentless monitoring of the Guest RAM metrics is one of the new feature introduced with vRealize Operations 6.3 with vSphere 6.0 U1. I was really happy to finally see this functionality, as memory metrics which are provided by default are not accurate and I would say almost useless when trying to right sizing your VMs.
Active memory metric (old one) is telling you about memory which was accessed by VM during some interval, but it says nothing about real usage. Especially if you want to prevent swapping (which you should in the virtualized environments with shared storage) of the idle pages. Swapping is what will happen most of the time, if you downsize your VM based on the active memory metric only and completely ignore construct of the memory usage inside the VM.
However I had big troubles to get this functionality working, it was working for some hosts only in one vCenter and not at all in another. I engaged VMware support and it tooks them “only” 4months to figure it out, but luckily they did.
- you need to have vCenter 6.0 U1, ESXi 6.0 U1, VMware tools from 6.0U1 (this part was easy)
- verify if you have enabled collection of the new metrics (easy part as well)
- Tricky one: As those metrics are internal, its collection by vCenter is not enabled by default. In this case you need to have special permission configured for an account which you are using for connection to your vCenter:
according to the support this is needed only once, when you are registering vCenter Adapter. If you have your vCenter Adapter already registered you need to restart it.
I recommend you to check out http://virtual-red-dot.info, which is great blog about vRealize Operations.
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