Menninger notes that Hadoop installations are much larger than you might think:
How big is “big data”? In his opening remarks, Mike shared some statistics from a survey of attendees. The average Hadoop cluster among respondents was 66 nodes and 114 terabytes of data. However there is quite a range. The largest in the survey responses was a cluster of 1,300 nodes and more than 2 petabytes of data. (Presenters from eBay blew this away, describing their production cluster of 8,500 nodes and 16 petabytes of storage.) Over 60 percent of respondents had 10 terabytes or less, and half were running 10 nodes or less.
(in the above quote, "Mike" is Mike Olson of Cloudera.)
Curt Monash has been keeping track of some of these stupendous database installations, and shares some of what he's learned in this note.
At my day job, we had an internal presentation the other day from one of our larger customers, who reported that they've constructed a single node with 3 terabytes of RAM-SAN as a cache ahead of their main database disk array.
Our customer didn't think that was particularly large. They were just noting that it was plenty large enough for their use, at the moment.