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Comment by JohnHaugeland | Hacker News Reader

They go to great effort to tell prospective customers that it's extremely reliable, providing claims of obscene numbers of nines.

A real engineer should know better, but otherwise, it's people trusting what a major company claims.

If it was a fly by night organization I would totally agree with you, but Amazon is a major multinational. It seems to me as reasonable for an outsider to trust the claims they make as it is for me, a car industry outsider, to trust the claims that Chevrolet makes about my car.

Do you know how to properly quality evaluate everything in your life?

Hope you don't need a doctor, lawyer, or plumber soon.

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Amazon only claims "obscene number of nines" for S3 durability (99.999999999%). And this claim seems to be accurate: I've never seen a publicly reported case of anyone losing data. Anytime you read their forums about people reporting data loss, a typical response is AWS staff saying "we see delete requests for those objects on date X" with the users responding "oh, oops, we had this background delete process".

However, for EBS volumes, Amazon is very clear about the expected data loss rate:

"The durability of your volume depends both on the size of your volume and the percentage of the data that has changed since your last snapshot. As an example, volumes that operate with 20 GB or less of modified data since their most recent Amazon EBS snapshot can expect an annual failure rate (AFR) of between 0.1% – 0.5%, where failure refers to a complete loss of the volume. This compares with commodity hard disks that will typically fail with an AFR of around 4%, making EBS volumes 10 times more reliable than typical commodity disk drives."

I withdraw my position as apparently in error.

Thank you for the exceptionally clear counterpoint.

I don't remember ever seeing "obscene numbers of nines" claimed by Amazon. For S3, yes, but not EBS. The '9' character doesn't even appear once on http://aws.amazon.com/ebs/.

What it does say is this:

"As an example, volumes that operate with 20 GB or less of modified data since their most recent Amazon EBS snapshot can expect an annual failure rate (AFR) of between 0.1% – 0.5%, where failure refers to a complete loss of the volume.

Which to any engineer, "real" or otherwise, should be a pretty strong signal that something bad will happen.

Yep, I've been telling this to people for years, and they keep sticking their fingers in their ears because they think they're entitled to magic uptime by amazon.

The key to EBS is frequent S3 snapshots. The reliability issues of EBS only appears to the delta since your last S3 snapshot. Still... people use EBS w/o frequent S3 backups, amazingly.

Frequent snapshots only help you recover after a failure. RAID1 in software is a good way to prevent downtime, as well as potentially improve read speeds.

Not really, according to the EBS docs, they can pull missing blocks from EBS from S3. You shouldn't have to perform a restore. The uncertainty should only apply to the delta unless I'm mistaken.

> They go to great effort to tell prospective customers that it's extremely reliable, providing claims of obscene numbers of nines.

Where do they do this? All the docs I've seen are pretty clear that EC2/EBS stuff could disappear and that you have to plan a fault-tolerant system.

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