We will now cover some of the more common uses cases for Ceph and discuss some of the reasons behind them.

Ceph is the perfect match to provide storage to an OpenStack environment. In fact, Ceph currently is the most popular choice. OpenStack Cinder block driver uses Ceph RBDs to provision block volumes for VMs and OpenStack Manila, the Shared File System service (FaaS), integrates well with CephFS. There are a number of reasons why Ceph is such a good solution for OpenStack:

• Both are open source projects with commercial offerings
• Both have a proven track record in large-scale deployments
• Ceph can provide block, CephFS, and object storage, all of which OpenStack can use
• It is possible to deploy a hyper converged cluster with careful planning

If you are not using OpenStack or have no plans to use it, Ceph also integrates very well with KVM virtualization.

Due to the ability to design and build cost-effective OSD nodes, Ceph enables you to build large high-performance storage clusters that are very cost-effective compared with alternative options. However, due to the recommended 3x replication, storage efficiency as calculated against raw storage cannot match traditional RAID JBOD (short for Just a Bunch of Disks) on price or power consumption. However, a lot of the benefits surrounding availability and performance may still make this use case attractive. Erasure coding support for use with RBD's, which should be available by the Luminous release, will close this gap greatly. If your archival requirement allows you to store data in objects, then erasure pools will enable you to match RAID on price and is a very attractive solution.

By the very fact that the core RADOS layer is an object store means that Ceph excels at providing object storage either via the S3 or Swift protocols. If cost, latency, or data security are a concern over using public cloud object storage solutions, running your own Ceph cluster to provide object storage can be an ideal use case.

Using librados, you can get your in-house application to directly talk to the underlying Ceph RADOS layer. This can greatly simplify the development of your application and gives you direct access to highly performant reliable storage. Some of the more advanced features of librados, which allow you to bundle a number of operations into a single atomic operation, are also very hard to do with existing storage solutions.

A farm of web servers all need to access the same files so that they can all serve the same content no matter which one the client connects to. Traditionally, a high-availability (HA) NFS solution would be used to provide distributed file access but can start to hit several limitations at scale. CephFS can provide a distributed filesystem to store the web content and allow it to be mounted across all the web servers in the farm.

There are several interactions between CephFS and Samba, which have not been refined, meaning that the end solution would not work as well as expected. Samba can successfully be used to present a CephFS filesystem, but the lack of HA and stable snapshots means that it will often be a poor replacement. As of the publication of this book, this is not currently a recommended use case for Ceph.