This is a blog post my student Koral De Grussa wrote in November 2017 that I never got around to posting until now. So here is it. (Andrew Horler)
What is “rightsizing”?
Right sizing is about using the correct amount of resources and not over allocating them or under allocating them.
Why is it important?
Knowing how to correctly rightsize resources for both virtual machines and physical machines is important as resources cost money but resources allow your system to run efficiently.
If you under resource a machine it will run slow or even fail.
If you over resource a machine it will cost you money to have unnecessary resources lying around doing nothing.
Correctly rightsizing a virtual machine can help in the migration of that virtual machine to the cloud and potentially lower the costs of running it in the cloud.
Migrating an over-resourced machine to the cloud can use up unnecessary bandwidth, slow down the migration and cause money to be spent to accommodate the unused resources.
You should run a test report to find out what the rightsize for a virtual machine should be. This test should monitor your overall resource usage (CPU, Memory, Disk, Network) for a minimum of a month but could be beneficial to run up to a year depending on the usage of the servers.
The reason for this is that a server might only be busy for certain months and not at all busy other months. So if you only monitor resource usage on this server when its quiet it can give the wrong impression about what resources it really requires.
E.g. A finance server may be quite for 11 months of the year but then when accounts are due, the servers on the 12th month will be in high demand. To correctly rightsized it should be based on the busiest month to ensure it isn’t under resourced for the its most demanding month.