vCenter does not provide a lot of memory counters at the cluster level. From the following performance chart dialog box, you can see that the number of counters drop to just five. Counters related to contention such as Compression, Swap, and Latency are no longer available. The Latency counter would be especially useful to track at cluster level if you have a large environment.

The data is not available in real time. This means the data granularity is at 5-minute intervals, not 20 seconds. As the rollup is an average, it means any spike within a 5-minute period may not be visible. In practice however, most performance problems would still likely be detectable with 5-minute data points.

The counters do not take HA into account. For example, the Total counter sums all the host physical memory.

The Consumed memory does not take into account the host memory. So the memory used by VMkernel is not included. This is practically negligible as most ESXi hosts sport...