Loosely Coupled Scale-Out Architectures

By John Busch  |  Posted 2009-09-29 Print this article Print

Loosely coupled scale-out architectures

A modern Web 2.0 and cloud computing data center scale-out system architecture deployment has at the front a Web server tier and an application server tier (sometimes merged together), and in the back-end a reliable data tier, usually hosted by database servers, which are typically slow and expensive elements. They often operate at very low CPU utilization due to blocking on HDD accesses, lock serialization effects and low HDD capacity utilization due to having to minimize head movement to reduce access latencies. 

Between the Web server tier and the back-end server tier are a content-caching tier and specialized application services, which may perform generic functions such as search, ad serving, photo store/retrieval, authentication or specific functions for the enterprise. Completing a response to a customer interaction involves accessing a Web server, application servers, database servers and various other generic and specialized applications and servers.

Data centers generally require that user responses complete in less than a quarter second. A DRAM-caching tier, consisting of servers filled with DRAM, usually completes this. Customer information, data retrieved from slow databases and common user interaction results are cached in this DRAM tier so they can be accessed very quickly.

Since the performance of a site can be improved dramatically through extensive caching, many racks of caching servers are typically deployed, with each holding a limited amount of DRAM, so the data must be partitioned among the caching servers. IT staff need to carefully lay out the data between the caching servers, which typically operate at very low network and CPU utilization, as they are simply storing and retrieving small amounts of data.

When loosely coupled scale-out architectures are examined closely, it becomes clear that the database and caching tiers suffer from very low utilization, high power consumption and excessive programmatic and administrative complexity-all contributing to high TCO. 

Dr. John Busch is President, CEO and co-founder of Schooner Information Technology. John has more than 25 years of industry experience. Prior to Schooner, he was research director of computer system architecture and analysis at Sun Microsystems laboratories from 1999 through 2006. In this role, he led research explorations in chip multiprocessing, advanced multi-tier clustered systems for deployment of Internet-based services, and advanced HPC systems. He received the top President's Award for Innovation at Sun, and oversaw many division technology transfers. Prior to Sun, he was VP of engineering and business partnerships with Diba, Inc., and was general manager of the Diba division after Sun acquired Diba in 1997. From 1989 to 1994, he was co-founder and CTO/VP of engineering of Clarity Software, and led creation of advanced multimedia composition and communication products for Sun, HP and IBM computer systems. From 1976 to 1993, he led many successful R&D programs at Hewlett-Packard in Computer Systems Research and Development. John holds a Ph.D. in Computer Systems Architecture from UCLA, a Master's degree in mathematics from UCLA, a Master's degree in computer science from Stanford University, and attended the Sloan Program at Stanford University. He can be reached at dr.john.busch@schoonerinfotech.com.

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