Book Image

Mastering Ceph

By : Nick Fisk
Book Image

Mastering Ceph

By: Nick Fisk

Overview of this book

Mastering Ceph covers all that you need to know to use Ceph effectively. Starting with design goals and planning steps that should be undertaken to ensure successful deployments, you will be guided through to setting up and deploying the Ceph cluster, with the help of orchestration tools. Key areas of Ceph including Bluestore, Erasure coding and cache tiering will be covered with help of examples. Development of applications which use Librados and Distributed computations with shared object classes are also covered. A section on tuning will take you through the process of optimisizing both Ceph and its supporting infrastructure. Finally, you will learn to troubleshoot issues and handle various scenarios where Ceph is likely not to recover on its own. By the end of the book, you will be able to successfully deploy and operate a resilient high performance Ceph cluster.
Table of Contents (12 chapters)

Investigating PGs in a down state

A PG in a down state will not service any client operations, and any object contained within the PG will be unavailable. This will cause slow requests to build up across the cluster as clients try to access these objects. The most common reason for a PG to be in a down state is when a number of OSDs are offline, which means that there are no valid copies of the PGs on any active OSDs. However, to find out why a PG is down, you can run the following command:

ceph pg x.y query

This will produce a large amount of output; the section we are interested in shows the peering status. The example here was taken from a PG whose pool was set to min_size 1 and had data written to it when only OSD 0 was up and running. OSD 0 was then stopped and OSDs 1 and 2 were started.

We can see that the peering process is being blocked, as Ceph knows that the PG has newer data written to OSD 0. It has...