I’ve been working on some similar analysis with EC2 and other providers. I think the big missing point in this post (acknowledged by the author) is with regards to EBS optimized instances and provisioned IOPS where we’ve observed a dramatic improvement in IO consistency. Another interesting observation I've experienced is that performance consistency often declines using multi-EBS volume raid, likely due to variations in spindle tenancy or network latency variations. EBS test volumes were 300GB. Better performance/consistency is possible using larger EBS volume sizes.

Here are links to a couple summaries of the analysis I’ve done on EC2, Rackspace and HP. I plan on writing a blog post regarding this analysis soon.

Disk Performance: The value columns is a percentage relative to a baremetal baseline 15k SAS drive, where 100% signifies comparable performance. Benchmarks included in this measurement are fio (4k random read/write/rw; 1m sequential read/write/rw), fio – Intel IOMeter pattern, CompileBench, Postmark, TioBench and AIO stress:

http://dl.dropbox.com/u/20765204/1012-disk-io-analysis/disk-...

Disk IO Consistency: The value column is a percentage relative to the same baseline. A value less than 100 represents better IO consistency than the baseline. The value is calculated by running multiple tests on an instance, measuring the standard deviation of IOPS between tests, and comparing those standard deviations to the baseline. Testing was conducted over a period of a month on multiple instances in different AZs.

http://dl.dropbox.com/u/20765204/1012-disk-io-analysis/disk-...