Object Storage approaches for OpenStack Cloud: Understanding Swift and Ceph

“Many people confuse object storage with block-level storage such as iSCSI or FibreChannel (SAN), but there is a great deal of difference between them. While SAN exposes only block devices to the system (the /dev/sdb linux device name is a good example), object storage can be accessed only with a specialized client app (e.g., the box.com client app).

Block storage is an important part of cloud infrastructure. Its main use cases are storing images for virtual machines or storing a user’s files (e.g., backups of all sorts, documents, pictures). The main advantage of object storage is very low implementation cost  compared to enterprise-grade storage, while ensuring scalability and data redundancy. There seem to be a couple of widely recognizable implementations of object storage. Here we’ll compare two of them that can be interfaced with OpenStack…”

http://www.mirantis.com/blog/object-storage-openstack-cloud-swift-ceph/