I started using a new subscription yesterday and I seem to have already used 53.68 MB of my 128MB cache. In one day?!
However, if I look at my cache in the Azure management portal I am not using it at all!
So where has this 53MB of AppFabric Cache come from? Since I've only put my site live for less than 24hrs I was worried I was blazing through my 128MB/month allowance but then I thought about it logically for a moment. You don't use up a cache you just use it. It doesn't go anywhere.
How AppFabric Cache usage is calculated and billed
With this in mind it becomes obvious what has happened. I set my AppFabric cache up before I got around to deploying my site. So really it has been used since 22nd December, which is 13 days ago. It is irrelevant that I have deployed a site onto it only yesterday.
Look at the maths: 128MB/31days = 4.13MB/day * 13days = 53.68MB. It is a confusing way of displaying it but still, it makes sense.