Yes, active memory is "Amount of memory that is actively used, as estimated by VMKernel based on recently touched memory pages" ... if you go to the advanced charts and select the counter it will show you the description.
I would look at consumed, in relation to granted (and ballooned as well). If you select the VM and then the resource allocation tab you will see a nice summary of this information.
Here is an example of a MSSQL server ... consuming most of the granted memory (as expected) - this matches upto what is seen in the guest ... but only 655.00 MB is Active, which matches upto the memory chart (Performance tab, overview).
Message was edited by: Jon Munday -- example added.
So if granted memory is 10GB for example, and consumed is also almost 10GB - does the vm need more memory???
On almost every vm the amount of consumed memory is the same as granted memory....
It sounds like they are sized appropriately as they are using what is allocated without paging or ballooning (especially since your active memory is low in relation to the granted memory).
What OS and applications are running on these VM's? If you're running SQL server, then this will (by design) use all available memory unless configured differently.
We're running Windows Server 2008 R2 and 2012 R2, some with SQL instances...
so we dont have to worry if our MONITORING (System Center Configuration Manager) is saying some servers are out of memory (>90% memory usage), but on the esxi server no ballooning is active?!
So How can I identify a VM has not engough memory?