Why do I need more disk space than the combined size of my projects?

A part of running Domino outside of our cloud offering (either on premise or in your own Amazon VPC) is determining how much disk space to allocate to hardware tiers. One important aspect to consider is the input/output (I/O) speed of your drives. In AWS, there’s a linear relationship between I/O speed and disk size. We often see customers who are I/O bound - where their ability to transfer data is a bottleneck which results in additional costs from longer run times.

We recommend admins determine disk space not by the size of the projects they’ll be working with, but by the number of input/output operations per second (IOPS) desired. If you need to do more reads and writes of data you need a larger disk to get the necessary headroom.  Commonly, we see that buying a larger, more expensive disk with faster IOPS ends up costing less than a smaller, slower disk, which takes more time to do the same amount of work.

You can read more details about Amazon RDS here - the table below shows how IOPS scales with disk size: