See conference video - http://www.lucidimagination.com/devzone/events/conferences/ApacheLuceneEurocon2011
Loggly is a cloud based logging service. It helps you collect, index, and store all your log data and then makes it accessible through search for analysis and reporting. All this is done without having to download or install anything on your servers. We have hundreds of customers, each of whom may have dozens of shards, quickly growing to thousands of individual indexes. To manage this explosion of indexes, I'll describe how we're using Solr Cloud to manage each and every index - from creation, through migration from box to box, and finally destruction. I'll describe some of the performance issues we had to deal with, especially with ZooKeeper.