Book Image

Ceph: Designing and Implementing Scalable Storage Systems

By : Michael Hackett, Vikhyat Umrao, Karan Singh, Nick Fisk, Anthony D'Atri, Vaibhav Bhembre
Book Image

Ceph: Designing and Implementing Scalable Storage Systems

By: Michael Hackett, Vikhyat Umrao, Karan Singh, Nick Fisk, Anthony D'Atri, Vaibhav Bhembre

Overview of this book

This Learning Path takes you through the basics of Ceph all the way to gaining in-depth understanding of its advanced features. You’ll gather skills to plan, deploy, and manage your Ceph cluster. After an introduction to the Ceph architecture and its core projects, you’ll be able to set up a Ceph cluster and learn how to monitor its health, improve its performance, and troubleshoot any issues. By following the step-by-step approach of this Learning Path, you’ll learn how Ceph integrates with OpenStack, Glance, Manila, Swift, and Cinder. With knowledge of federated architecture and CephFS, you’ll use Calamari and VSM to monitor the Ceph environment. In the upcoming chapters, you’ll study the key areas of Ceph, including BlueStore, erasure coding, and cache tiering. More specifically, you’ll discover what they can do for your storage system. In the concluding chapters, you will develop applications that use Librados and distributed computations with shared object classes, and see how Ceph and its supporting infrastructure can be optimized. By the end of this Learning Path, you'll have the practical knowledge of operating Ceph in a production environment. This Learning Path includes content from the following Packt products: • Ceph Cookbook by Michael Hackett, Vikhyat Umrao and Karan Singh • Mastering Ceph by Nick Fisk • Learning Ceph, Second Edition by Anthony D'Atri, Vaibhav Bhembre and Karan Singh
Table of Contents (27 chapters)
Title Page
About Packt
Contributors
Preface
Index

Scrubs


Data corruption is rare but it does happen, a phenomenon described scientifically as bit-rot. Sometimes we write to a drive, and a surface or cell failure results in reads failing or returning something other than what we wrote. HBA misconfiguration, SAS expander flakes, firmware design flaws, drive electronics errors, and medium failures can also corrupt data. Surface errors affect between 1 in 1016 to as many as 1 in 1014 bits stored on HDDs. Drives can also become unseated due to human error or even a truck rumbling by. This author has also seen literal cosmic rays flip bits.

Ceph lives for strong data integrity and has a mechanism to alert us of this situation: scrubs. Scrubs are somewhat analogous to fsck on a filesystem and the patrol reads or surface scans that many HBAs run. The idea is to check each replicated copy of data to ensure that they're mutually consistent. Since copies of data are distributed throughout the cluster this is done at Placement Group (PG) granularity...