Distributed Storage Systems for Linux?

elambrecht asks: "We've got a _lot_ of data we'd like to archive and make sure it is accessible via the web 24/7. We've been using a NetApp for this, but that solution is just waaaay to expensive to scale. We want to move to using a cluster of Linux boxes that redundantly store and serve up the data. What are the best packages out there for this? GFS? MogileFS?"