Amazon and 11 nines

Amazon has claimed 11 nines on Availability . It is very very hard feast to accomplish, and if they have done it (I would love to know how they decided on that number), that is a ground breaking achievement.

To see why, lets see what it means. Availability is measured as MTTR (Mean time to Recovery)/ MTTF (Mean time to Failure) as a percentage. In other words, it is time to recover after a failure, divided by mean time for such a failure happen. Reliability is measured in terms of number of nines in availability. So Amazon S3 will be fail for a second only for every 10^9 seconds, or 10^9/(360*24*60*60) = 32 years!!

On their seminal paper "High Availability Computer Systems", Jim Gary and Daniel Siewiorek defined availability classes, as follows

unmanaged 90.% - 50,000 mins/year downtime

managed 99.% - 5,000 mins/year downtime

well-managed 99.9% - 500 mins/year downtime

fault-tolerant 99.99% - 50 mins/year downtime

high-availability 99.999% - 5 mins/year downtime

very-high-availability 99.9999% - .5 mins/year downtime

ultra-availability 99.99999% - .05 mins/year downtime

As you will notice even they defined only 7 nines. So we do not have a name to call what Amazon has claimed.

Squirrel near our backdoor

Squirrel near our backdoor
Originally uploaded by Srinath Perera

WSO2 Stratos Services Released

WSO2 Stratos, which offers WSO2 SOA platform as a service, is now live, up and running. Stratos opens up a new deployment choice for our servers, by enabling them have their servers as a Service. For example, if a user need a Governance Registry, he had to either run it real hardware, run it through a Virtual Machine, or run it through Cloud. Now, there is a forth option: that is get it as a service through WSO2 Stratos. Of course there is much more to Stratos, see http://wso2.com/cloud/stratos/ and The Six Weeks and 12 People Magic for some more details.

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