The Ceph storage technology used by DreamObjects stores multiple copies (three copies, I think?) of uploaded files, with each copy kept separate from the others. I'm not certain how we have it configured, but my understanding is that it's configured to not just keep each copy on a different hard drive, but also on a different machine, or even in a different section of the data center.
Soon. But keep in mind that bandwidth for files downloaded through the CDN will likely be more expensive than files downloaded through DreamObjects directly.