Block storage itself is a very old idea. Hard drives (and other storage media) present themselves to operating systems as a collection of blocks, each of which store data. The operating system is responsible for turning those blocks into something that applications can use. So when people say “block storage,” what they’re really talking about is storage that behaves like a hard drive.
“Cloud block storage is block storage that’s been built to integrate with cloud platforms. Usually cloud block storage is distributed across many computers and many hard drives,” explained Ross Turk, the VP of Community at Inktank, the commercial support company behind the open source storage project, Ceph.