High Scalability has tested cloud storage services for scalability based on load. As a test, they used the common test TPC-W . For testing, the load was gradually increased from 1 user to 9,000 concurrent users. The following services took part in testing: a full-fledged relational SQL Azure DBMS, Amazon S3, Amazon RDS, Amazon SimpleDB, Google AppEngine.
Test results:
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Obviously, SQL Azure, being a complete relational database, shows excellent results. On the opportunities + scalability - this is definitely the leader of testing. The Google service turned out to be an outsider of the testing.