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I'm doing capacity planning for my DR site and i'm trying to understand break-even point for Light/Medium/Heavy reserved instances vs the Ondemand. I have plotted my values on a graph as shown in the picture below:

http://imgur.com/wLAOIX1

Am i correct,in making the following assertions ?

  1. For an m3.large instance running 24/7 (100% utilization),there is no break-even point and does it makes sense to prefer an Ondemand over light RI ?

  2. The break-even point for a High RI over Ondemand is some where around 170 days. Am i right in saying,choosing High RI pays dividends only if,the uptime of that instance is more than 170 days or 4080 Hours (46.44 %) in an year?

Michael Hampton
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hmmm
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1 Answers1

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If you're using it 100% of the time, use heavy utilization for the highest discount rates. However, if it's going to be a disaster recovery solution, you might as well use "light utilization" unless the higher price (for longer periods) and uncertain capacity of on-demand is enough for you.

The major difference is that with on demand, you're not promised capacity, so it can throw your entire DR setup out the window, hence why reserved instances exist. However, the upfront cost is a deterrent...

Nathan C
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