Memory usage in the Esxi server is around 90%, but memory usage is not much in virtual servers. what is the reason for this difference? I am considering purchasing memory for physical servers. I couldn't decide whether to buy memory or not. If I buy it can you tell me why? Do you think physical servers need memory and why? must i add physical memory to the host ?
dd physical memory to the host?
i use esxi 5.1
this is most likely the result of the fact that the UI shows "consumed memory", which would include all pages which are touched by the Operating System during the boot of the VM. As a result it will look like you are consuming all memory available. Check "active" to figure out if you are indeed close to reaching those limits.
How will I know if I will need physical ram. I could not fully understand your answer.
this is a pretty old article, but it should help:
http://www.yellow-bricks.com/2011/04/29/which-metric-to-use-for-monitoring-memory/
Look at "active" basically, that should give some indication if you need to increase memory or not.
How are your VMs performing? If everything is running well, you are not planning on adding more VMs, and your VMs will not be increasing their memory usage, then I would not buy more memory if I was you.