

Raising the Roof - More Provisioned IOPS for EBS - jeffbarr
http://aws.typepad.com/aws/2012/11/raising-the-roof-more-provisioned-iops-for-ebs.html

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po
Here's my question about IOPS that I can't seem to find the answer to:

I get that if you have a workload that needs 1000 IOPS and you only have
500IOPS QOS provisioned, then they will get queued and you will see latency.
However, if you have a workload of 500IOPS needed and you have 1000IOPS QOS
provisioned, what is the latency of that? Moreover, what is the variance of
the latency of that?

Basically, if they are saying you get a 20 lane highway and you're guaranteed
to get 200 cars a second across it, that doesn't mean that if you only have 10
cars that they're going to come through quickly. The quote they highlight
talks about latency:

 _Amazon's Provisioned IOPS helped us improve our MongoDB query speed by over
60% and drastically reduced latency spikes to our clusters. We are thrilled to
welcome the new 2000 P-IOPS volumes._

… but does the EBS PIOPS SLA talk about latency or variance in latency when
you're below that number at all? Is it true that EBS really only experiences
latency variation when you go over your provisioned IOPS?

Maybe I'm thinking about this the wrong way…

 _edited to add:_ After thinking about this some more I guess what I wanted to
ask is: I have a database and I want to put it on EBS. If it doesn't even need
100 IOPS but I still want extremely low latency and latency variance, do AWS
Provisioned IOPS guarantee this?

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lacker
Hi, I'm the guy from Parse who is quoted in that article. Amazon's description
of provisioned IOPS doesn't precisely guarantee low latency and latency
variance for small numbers of IOPS. However, that's exactly what we've found
in practice. I would definitely recommend the PIOPS if you're concerned with
latency and consistency - it does not work like EBS.

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po
Thanks for the clarification. That's sort of what I had gathered but it's
useful to know exactly what is guaranteed and what isn't.

