Let me explain about the AWS free usage tier.

EBS devices are block devices.

This means the service does not know how much data we actually store on them, it only knows how much storage space we have allocated.

So the result of df -h doesn’t matter. Actually we are only using 16GB of storage out of 30 GB.

The actual size of the volume is all that matters and that’s the basis for billing. This means it will calculate whole 30GB here.

Now, the free tier allows 30 gigabyte-months of EBS volume usage. You can use more than that, but this is the limit that’s provided for free. You’ll be billed for any more than this.

A gigabyte-month means 1 gigabyte of block storage space, allocated for 1 month, regardless of how you use it.

2 gigabytes of allocated storage for 15 days is 1 GB-month.

10 gigabytes of allocated storage for 3 days is 1 GB-month.

The free tier would allow

30 GB volume for 30 days

60 GB volume for 15 days or

900 GB volume for only 1 day.

To recapitulate ->

If we have a 30 GB volume for 26 days, then we have used 26 GB-months of storage, which is 86.7% of the free tier limit of 30 GB-months.

This is the logic that applies to all the services. Actually it is charged per-second basis now.

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