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How does Elastic File System affect AWS storage costs?

Amazon only charges for actual storage capacity incurred in its new Elastic File System service. Fine, but what is the final price for the service?

With Amazon Elastic File System, users pay only for the storage capacity that is actually used. But it is still...

important to consider how charges occur.

AWS Elastic File System (EFS) is currently priced at $0.30 per "gigabyte-month" (GB-month) without minimum purchases or setup fees. That might sound simple, but calculating the actual AWS storage costs for EFS can be difficult.

Suppose that your EFS instance uses 100 GB for an entire 31-day month. In this case, the calculation would be straightforward at 100 GB-months: (100 GB x 31 days x 24 hours/day) / (744 hours/month). But calculations become more complicated as storage use varies throughout the month. For example, if a company used 300 GB for 15 days and only used 200 GB for the remaining 15 days of a 30-day month, the calculation for EFS pricing would look something like this:

(300 GB x 15 days x 24 hours/day) + (200 GB x 15 days x 24 hours/day)

This would be:

108,000 GB-hours + 72,000 GB-hours = 180,000 GB-hours

Then, with 720 hours in a 30-day month:

180,000 GB-hours / 720 hours/month = 250 GB-months @ $0.30/GB-month = $75 for the month.

As another example, suppose that you used 100 GB for 10 days, 150 GB for another eight days and 230 GB for the final 13 days of the 31-day month. The calculation for EFS pricing would look something like this:

(100 GB x 10 days x 24 hours/day) + (150 GB x eight days x 24 hours/day) + (230 GB x 13 days x 24 hours/day)

This would be:

24,000 GB-hours + 28,800 GB-hours + 71,760 GB-hours = 124,560 GB-hours

Then, with 744 hours in a 31-day month:

124,560 GB-hours / 744 hours/month = 167.42 GB-months @ $0.30/GB-month = $50.22 for the month

Varying daily storage use can become difficult to track manually. However, there is no hard limitation to the amount of storage capacity available for EFS. Amazon notes that EFS is designed to support petabyte-scale storage instances and support connections for thousands of concurrent sessions using the Network File System version 4 (NFS v4).

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This was last published in July 2015

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How has your enterprise saved on storage costs?
Because almost all jobs in our company are one-offs, it's fairly easy for us to off-load our data onto some form of permanent storage media leaving little data in the cloud. Then we start again. Our data stored is highly variable from day to day. Calculating the daily cost of storage seems complicated, but it's just basic math. If I were smarter, I'm sure I could come up with a neat formula to simplify the process.
How granular do we go here? Is it any less than a day? or do you pay the full day's worth even if you've only been using the storage for a few hours?