Amazon EBS volumes are billed by the gigabyte-month (GB/m).
So this limit of 30 GB is for a month. Anything exceeding this will be charged.
In a 31-day month, you are billed for one gigabyte-month in the following scenarios:
- If you have a 31-GB volume that was active for 24 hours.
- If you have a 1-GB volume that was active for 744 hours (the number of hours in 31 days).
- EC2 instances accrue charges only while they're running, but EBS volumes attached to instances continue to retain information and accrue charges, even when the instance is stopped.
- You can provision your EBS volume in the 3 instances in such a way that the total volume does not exceed 30 GB.( eg: 8+8+8 )