[From Linux Magazine]
In the last year a handful of MySQL and memcached appliances have appeared on the market. These tend to be 2U rackmount servers that you treat as a black box (or something approaching one) and reap some sort of substantial performance benefit along the way. Most of these appliances have a mix of commodity hardware and some “special sauce” on both the hardware and software layers. In addition, there are specialized storage devices aimed squarely at improving MySQL performance that you can drop into your commodity servers, thus making your own appliance.
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http://www.linux-mag.com/cache/7453/1.html