Tuesday, August 11, 2009 |
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Microsoft has yet to release all the details of its Azure SLA, but it has said that you will have a 99.95 per cent up-time for compute and 99.9 per cent up-time for SQL Azure.
How does this compare with my electric utility?
With my latest electric bill, my local utility listed its 2008 average number of service interruptions per customer as 1.051, and the average number of minutes without power for a customer at 78.55 minutes. So my electric utility has an up-time of .9998. I guess they don't get 4 or 5 "9"s either.
I presume these numbers include outages due to winter storms, but I do not know what the utility regulators allow them to exclude. Microsoft, to my knowledge, has not stated whether the SLA percentages include planned downtime for upgrades.
How many outage minutes per year could we expect with Azure under the SLA? That comes to about 262.8 compute minutes per year, or about 4.36 hours. Of course when those outages occur matters, and whether they are concentrated in one or many interruptions.
For SQL Azure that SLA is on a per month basis. So for data you could loose access to it for 43.8 minutes per month.
Is 4 hours a long time? Could you live without data access for 45 minutes a month?
For Facebook probably, for emergency services you would need some sort of fallback just like they have backup generators now.
I wonder what a cloud computing brownout looks like?
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