Ceph is an open source, distributed, scaled-out, software-defined storage system that can provide block, object, and file storage. Through the use of the Controlled Replication Under Scalable Hashing (CRUSH) algorithm, Ceph eliminates the need for centralized metadata and can distribute the load across all the nodes in the cluster. Since CRUSH is an algorithm, data placement is calculated rather than based on table lookups, and can scale to hundreds of petabytes without the risk of bottlenecks and the associated single points of failure. Clients also form direct connections with the required OSDs, which also eliminates any single points becoming bottlenecks.

Ceph provides three main types of storage: block storage via the RADOS Block Device (RBD), file storage via CephFS, and object storage via RADOS Gateway, which provides S3 and Swift-compatible storage.

Ceph is...

The core storage layer in Ceph is the Reliable Autonomous Distributed Object Store (RADOS), which, as the name suggests, provides an object store on which the higher-level storage protocols are built. The RADOS layer in Ceph consists of a number of object storage daemons (OSDs). Each OSD is completely independent and forms peer-to-peer relationships to form a cluster. Each OSD is typically mapped to a single disk, in contrast to the traditional approach of presenting a number of disks combined into a single device via a RAID controller to the OS.

The other key component in a Ceph cluster is the monitors. These are responsible for forming a cluster quorum via the use of Paxos. The monitors are not directly involved in the data path and do not have the same performance requirements of OSDs. They are mainly used to provide a known cluster state, including membership...

Before jumping into specific use cases, let's look at the following key points that should be understood and considered before thinking about deploying a Ceph cluster:

• Ceph is not a storage array: Ceph should not be compared to a traditional scale-up storage array; it is fundamentally different, and trying to shoe horn Ceph into that role using existing knowledge, infrastructure, and expectations will lead to disappointment. Ceph is software-defined storage with internal data movements that operate over TCP/IP networking, introducing several extra layers of technology and complexity compared to a simple SAS cable at the rear of a traditional storage array. Work is continuing within the Ceph project to expand its reach into areas currently dominated by legacy storage arrays with support for iSCSI and NFS, and with each release, Ceph gets nearer to achieving...

While considering infrastructure design, we need to take care of certain components. We will now briefly look at these components.

SSDs are great. Their price has been lowered enormously over the last 10 years, and all evidence suggests that it will continue to do so. They have the ability to offer access times several orders of magnitude lower than rotating disks and consume less power.

One important concept to understand about SSDs is that, although their read and write latencies are typically measured in tens of microseconds, to overwrite existing data in a flash block, requires the entire flash block to be erased before the write can happen. A typical flash block size in an SSD may be 128k, and...

The following are some general rules for deploying a successful Ceph cluster:

• Do use 10 G networking as a minimum
• Do research and test the correctly sized hardware you wish to use
• Don't use the no barrier mount option with filestore
• Don't configure pools with a size of two or a min_size of one
• Don't use consumer SSDs
• Don't use raid controllers in write back mode without battery protection
• Don't use configuration options you don't understand
• Do implement some form of change management
• Do carry out power-loss testing
• Do have an agreed backup and recovery plan

As we have discussed, Ceph is not...

In this chapter, you learned all of the necessary steps to allow you to successfully plan and implement a Ceph project. You also learned about the available hardware choices, how they relate to Ceph's requirements, and how they affect both Ceph's performance and reliability. Finally, you also learned of the importance of the processes and procedures that should be in place to ensure a healthy operating environment for your Ceph cluster.

The following chapters in this book will build on the knowledge you have learned in this chapter and help you put it to use to enable you to actually deploy, manage, and utilize Ceph storage.

1. What does RADOS stand for?
2. What does CRUSH stand for?
3. What is the difference between consumer and enterprise SSDs?
4. Does Ceph prefer the consistency or availability of your data?
5. Since the Luminous release, what is the default storage technology?
6. Who created Ceph?
7. What are block devices created on Ceph called?
8. What is the name of the component that actually stores data in Ceph?