Chapter 4. OpenStack Object Storage Service Installation

4.1. Object Storage Service Overview

The Object Storage service provides a storage system for large amounts of data, accessible through HTTP. Static entities such as videos, images, emails, files, or VM images can all be stored. Objects are stored as binaries on the underlying file system (using metadata stored in the file’s extended attributes, xattrs). The service's distributed architecture supports horizontal scaling; redundancy as failure-proofing is provided through software-based data replication.
Because the service supports asynchronous eventual consistency replication, it is well suited to multiple data-center deployment. Object Storage uses the concept of:
  • Storage replicas, which are used to maintain the state of objects in the case of outage. A minimum of three replicas is recommended.
  • Storage zones, which are used to host replicas. Zones ensure that each replica of a given object can be stored separately. A zone might represent an individual disk drive or array, a server, all the servers in a rack, or even an entire data center.
  • Storage regions, which are essentially a group of zones sharing a location. Regions can be, for example, servers or server farms usually located in the same geographical area. Regions have a separate API endpoint per Object Storage service installation, which allows for a discrete separation of services.
The Object Storage service relies on other OpenStack services and components. For example, the Identity Service (keystone), the rsync daemon, and a load balancer are all required.

Table 4.1. Object Storage Service components

Component Description
Exposes the public API, provides authentication, and is responsible for handling requests and routing them accordingly. Objects are streamed through the proxy server to the user (not spooled).
Stores, retrieves, and deletes objects.
Responsible for listings of containers, using the account database.
Handles listings of objects (what objects are in a specific container), using the container database.
Ring files
Contain details of all the storage devices, and are used to deduce where a particular piece of data is stored (maps the names of stored entities to their physical location). One file is created for each object, account, and container server.
Account database
Stores account data.
Container database
Stores container data.
ext4 or XFS file system
Used for object storage.
Housekeeping processes
Replication, auditing, and updating processes.