Not really, Block systems are just glorified key:value databases.

Here are a few scalable open source block/object storage systems:

Lustre

Ceph

tahoe-lafs

XtreemFS

These are all opensource.

For example, if I wanted a fast global-coherent CDN, then all I need are webservers and GPFS, with some glue code to allow auth'd uploads/deletes. geographically scalable, with tiered storage levels.

If you want to run on dodgy hardware, then use XtreemFS. but you'll pay a performance price.

I'd be interested in a comparison in developer language(as in graphs code examples etc.), with a github link or similar.