Hey, Some months ago (last year!!) during our previous major upgrade from 1.1 -> 1.2 I started writing a blog post with some tips for a smooth rolling upgrade, but for some reason I forgot to finish the post. I found it recently and decided it to publish anyway, as some of the info may be helpful for future major upgrades:
http://monkeys.chaordic.com.br/operation/zero-downtime-cassandra-upgrade/ Cheers, -- *Paulo Motta* Chaordic | *Platform* *www.chaordic.com.br <http://www.chaordic.com.br/>* +55 48 3232.3200