Memory metrics

RAM could be overcommitted (assigning VMs more memory than the host physical RAM) on an ESXi host, and this was one of the historical advantages of VMware products. However, just because you can, it does not necessarily mean that you should.

Now, in most cases, it is not recommended anymore because it will degrade the performance of your environment (for example, memory ballooning or swapping also have an impact on storage). So, the right memory sizing could be really important, not only for the workload but also for high-availability aspects (we will discuss this more in Chapter 13, Advanced Availability in vSphere 6.5).

Note also that there are more and more workloads that are becoming more memory bound—consider, for example, all in-memory databases. In those cases, you should design the hosts carefully and maybe consider a specific cluster for those workloads (depending on the numbers and the recommended practices from the software vendor).

For memory, the following table suggests some possible metrics:

Table 3.2: Some possible metrics for memory