How is Amazon S3 storage billed?

Question

Various Amazon S3 questions

Hey everyone,

I just got an Amazon S3 account and I am developing my production backup script / strategy and just had a few questions.

• Monthly Storage - how exactly is this measured, and when? Is it a snapshot based thing where at a particular time your usage is measured? IE what is stopping someone from keeping a 2GB file there for 29 days out of the month, then deleting it when billing comes around? I would assume this is pro-rated or something?
• Rates - "$0.150 per GB - first 50 TB / month of storage used" . To confirm - if i keep 2GB of data in my bucket for one month, my bill is $0.30, but if I clean it out to be only 1GB when next month comes around, my bill will drop to $0.30? This sort of ties in to my last question about at what point storage is measured.
• FTP - there is no FTP access to my buckets at all? How come this is restricted?

Edit: One last one - I know it is WIDELY used, but just how reliable is this service? Are there any guaruntees that Amazon offers upon sign up? Has it ever gone down?

Thank you,

Answer 1

Storage / Rates: "The GB of storage billed in a month is the average storage used throughout the month. This includes all object data and metadata stored in buckets that you created under your account. We measure your usage in “TimedStorage-ByteHrs,” which are added up at the end of the month to generate your monthly charges."

FTP: Because it would be silly, as the storage model does not work this way.

Answer 2

Amazon is generally considered to be pretty reliable. Their own CDN runs their (vast) enterprise, so they do know what they're doing. Read the SLA on their site, it will tell you exactly what they promise (which is, as others have pointed out, less complete coverage than might be desired). You might consider adding another CDN at some point down the road if you want greater availability.

As far as billing, as the others have said, it's a rolling average. You're billed monthly for your average use which is sampled hourly.

The reason they don't offer FTP is that their service is not based on a traditional file system model. It's essentially a huge database, with key/value pairs. They run frontend software that lets you access something in the database by giving its key to a webserver, which fetches it from the actual content storage device. There's no traditional hierarchical filesystem involved at any point.

That said, there are a number of easy-to-use insertion tools which let you put your files in with little effort.

Answer 3

As for reliablity when you signed up for it you no doubt had the opportunity to read the SLA. It states the following

*Service Commitment

AWS will use commercially reasonable efforts to make Amazon S3 available with a Monthly Uptime Percentage (defined below) of at least 99.9% during any monthly billing cycle (the “Service Commitment”). In the event Amazon S3 does not meet the Service Commitment, you will be eligible to receive a Service Credit as described below.*

Which means it could be down like 1 minute 26 seconds in a day or 8 hours 45 minutes 57 seconds in a year. Otherwise they'll give you a service credit.