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Comment by cperciva | Hacker News Reader

Right. But it matters how much availability drops, and also what the correlation is between failures -- if they're completely uncorrelated but there's a 1% failure rate, you just retry, but if 1% of objects are going to be unavailable for the next four hours, that's a problem.

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From one of the customer quotes on the page:

> it’s vital that customers have immediate, instant access to any of [our photos] at a moment’s notice – even if they haven’t been viewed in years. [IA] offers the same high durability and performance ... so we can continue to deliver the same amazing experience for our customers.

The way this was phrased implies that this customer's use-case had a hard requirement that all of their data be in "online" storage at all times, and their satisfaction implies that IA does, in fact, hit this requirement.

I'm not sure what the 99% SLA means given that.

Huh, I hadn't noticed that quote. Now I'm really confused.

To me it sounds like:

S3 Classic: Your file gets replicated on 3 live HDs (and/or HDs backed by RAID arrays—not sure about the internal S3 storage topology).

S3 Infrequent: Your file gets stored on 1 live HD (or single hardware redundancy component) and a copy in Glacier. If your live HD dies, your file will be automatically restored from Glacier to a new HD (but your data may be inaccessible during the automatic re-deploy).

Glacier: offline bluray combined with error correction accessed by robot arms, temporarily restored to live HDs on demand.

I thought Glacier used "green" consumer drives clocked down even further to save power?

Whichever they use, most disks are likely unpowered most of the time. Like the Facebook equivalent where they can only power 1 out of 12 disks at any time.

I understand that 99% doesn't mean that 1% of the objects will be always unaccesible. Instead, I guess that they mean is that they allow themselves to have up to 80 hours a year of downtime for any bucket.

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