One of the most common requests in relation to vSAN performance is how much CPU and memory does vSAN actually consume on an ESXi host, i.e. what is the overhead of running vSAN. Through the vSAN Performance Service, we have been able to show both host and vSAN CPU usage for some time. However, up to now, we have only been able to show host memory usage, and not overhead attributed to vSAN. It has also been extremely difficult to determine how much memory vSAN required. Way back in 2014, with the first vSAN version 5.5 release, I wrote this article on the relationship between disks, disk groups and memory requirements. In vSAN 6.x, I wrote another article detailing how these memory overhead calculations had changed with newer releases of vSAN. There was even a knowledge base article written to help you figure out the math for the overhead – in a nutshell, it wasn’t easy. However, none of these posts or KB articles really helped you to see exactly how much memory vSAN was consuming on an ESXi host after it was enabled. Well, in vSAN 7, I’m delighted to see a new metric added to the Performance for Support graphs which details exactly how much memory vSAN is consuming on a per ESXi host basis.
To find this new metric, simply navigate to your vSAN 7 cluster, select Monitor > vSAN > Support > Performance for Support. Then, from the Performance Dashboards drop-down, under More Dashboards, select Memory > vSAN Memory. Whilst Performance for Support metrics exist in previous versions of vSAN, the vSAN Memory metric does not. Here is a view of vSAN 6.7U3 compared to vSAN 7.
And if we select the vSAN Memory metric in the vSAN 7 cluster, we see exactly how much memory overhead can be attributed to vSAN on a per host basis.
Now customers will be very easily able to observe how much additional memory is consumed by vSAN as more storage devices are added to disk groups or new disk groups are added to hosts. As well, customers will be able to observe the memory overhead when enabling vSAN storage services such as deduplication or compression. I know that this is a feature that will delight many vSAN customers.