Understanding Dashboard

There is a subtle yet important difference between real time usage vs the allocated view of cloudstack. Allocated capacity refers to the resources reserved by MS.
So for example if your MS has the following configuration : 2GB RAM, 2GHZ CPU, 10GB storage Lets say you choose a service offering of 1GB RAM and 1GHZ CPU and 5gb disk for deploying a vm, MS then reserves these capacities from its physical resources exclusively for this vm. While the vm's actual usage might be significantly less (say .1gb RAM , 128MHZ CPU and 1 gb storage)than the allocated capacity. Assuming this to be the only vm in the system, the dashboard would display the following values.
Allocated RAM - 1/2 (50%)
Allocated CPU - 1/2 (50%)
Allocated Storage - 5/10 (50%)
Storage Used - 1/10 (10%)

Ideally we wouldn’t want to have a huge difference between allocated and real time usage and hence the notion of overprovisioning.

Also note that while deploying vm's we always consider the total allocated capacity and never the real usage of the resources.

The current granularity of dashboard is shows it till the cluster level. So though the aggregate view might show some vacant space there might be no physical resource in the cluster/pod/zone with enough space to accommodate the vm in terms of cpu, ram or storage.

Dashboard view is updated real time for cpu and ram and every 5 mins (capacity.check.period) for storage.