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)

Full OSDs

By default, Ceph will warn when OSD utilization approaches 85%, and it will stop write I/O to the OSD when it reaches 95%. If, for some reason, the OSD completely fills up to 100%, then the OSD is likely to crash and will refuse to come back online. An OSD that is above the 85% warning level will also refuse to participate in backfilling, so the recovery of the cluster may be impacted when OSDs are in a near full state.

Before covering the troubleshooting steps around full OSDs, it is highly recommended that you monitor the capacity utilization of your OSDs, as described in the monitoring chapter. This will give you advanced warning as OSDs approach the near_full warning threshold.

If you find yourself in a situation where your cluster is above the near full warning state, you have two main options:

  1. Add some more OSDs.
  2. Delete some data.

However, in the real world, both of these are either impossible...