Chapter 2. Understanding Swift

Swift is the oldest and probably the mature project within OpenStack. It is the underlying technology that powers Rackspace’s Cloud Files™ service. While it only interacts tangentially with Nova (as shown in Chapter 3), it is still important in the overall scheme of understanding OpenStack.

Swift aims to provide a massively scalable and redundant object store conceptually similar to Amazon’s S3 service. To provide this scalability and redundancy, it writes multiple copies of each object to multiple storage servers within separate “zones.” Zones are a logical grouping of storage servers that have been isolated from each other to guard against failures. The level of isolation is up to the cloud operator; they can be isolated on differing servers (ability to lose individual servers), different racks (ability to lose entire rack), different sections of the data center, or even different data centers. Each choice provides a different level of isolation and cost.


Many beginners assume that Swift will take the place of their file server and that they will be able to easily mount volumes on their desktops to access their files. This is not the case. Swift is an object store, not a file server. While these sound similar, there are important differences. Object stores simply save files in logical groupings (called “containers” in Swift parlance) via a RESTful protocol. They do not provide a true filesystem, nor are they accessible through standard file ...

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