Comment 3 for bug 938365

Here's some reworking of the text:

Object Storage in general (and swift specifically) provides large scale, cheap, and durable
storage. Swift is not used like a traditional hard drive - Object storage is all about
relaxing some of the constraints of a POSIX-style file system. The access to it is API-based (and the API uses http).

This is a good idea as if you don't have to provide atomic operations (ie you can rely on eventual
consistency), you can much more easily scale a storage system and avoid a central point of failure.

 The OpenStack Image Service is used to manage the virtual machine images in an OpenStack compute cluster
 and provide an abstraction to ways of storing them (a bridge to the storage, not the storage itself).
 Swift is one option that can be used by the OpenStack Image Service to store images, but it can function
 on its own.

nova-volume is for block storage attached to a virtual machine. Where Swift isn't a filesystm,
nova-volume is - designed to provide "mountable" devices.