In the previous chapter, we looked at managing block storage with Cinder. Block storage attaches directly to the instances, and the operating system on the instance writes to the filesystem. Object storage is an alternative storage option. Object storage is a simple form of storage that handles file operations on the instances by way of API calls. This decouples the operating system and the file storage. Swift is the object storage component in OpenStack. In this chapter, we are going to take a deeper look at what object storage is, how to use it, and some options available to use as the backend storage engine.
Object storage works by using a client to send and receive files to and from the object store. The files are stored with very little metadata and are treated as a whole entity. The object server does not work in partial pieces of an object the way block storage would work with file blocks. It is a very simple storage method focused on storing and retrieving the contents of the files with minimal overhead to the operating system while interacting with the storage server. The power of the Swift object storage engine is its robust software-defined storage backend. The Swift storage engine has distribution and replication capabilities across its storage nodes. First, let's take a look at the client side of using Swift, and later, we will look at the backend storage engine.