About CephClusterGuide

Distributed Ceph Storage, CRUSH Maps & RADOS Pool Guide

What this site covers

CephClusterGuide is an engineering reference for Ceph storage clusters. It covers the decisions made once and regretted for years: how data is placed, how much redundancy costs, and how the daemons behave when hardware fails.

• CRUSH map rules and failure domains
• Placement group sizing
• Erasure-coded versus replicated pools
• OSD daemon tuning
• RADOS pool configuration

7 articles are published so far. New ones are announced on the RSS feed.

Start here

Four decisions account for most of what a Ceph operator has to get right early, and each has a guide:

• How Ceph places data — OSDs, pools, placement groups, and what a CRUSH failure domain actually promises.
• Ceph hardware requirements — the published figures for OSD processors, memory, drives and networking, and which of them to exceed.
• Erasure coding versus replication — space amplification per profile, how many failure domains each needs, and why the choice is not reversible.
• Diagnosing HEALTH_WARN — a triage order for degraded placement groups, nearfull OSDs, missed scrubs and monitor clock skew.

There is also one interactive tool, the Ceph erasure coding calculator, which estimates raw capacity, theoretical usable capacity and default OSD memory targets from an OSD count, a drive size and a redundancy profile.

For a planned expansion, follow the guide to add an OSD to Ceph. It covers device checks, a cephadm preview and the health checks used to verify a rebalance.

How these articles are produced

Articles here are researched from primary sources: vendor and project documentation, published standards and specifications, research papers and preprints, and measurements published by whoever took them. Drafts are produced with AI assistance and then edited against those cited sources before anything is published.

No article on this site is based on first-hand testing in a private lab, and nothing here should be read as a measurement report of its own. Where a number appears, it comes from a source that is named, so you can check the original instead of taking this site's word for it.

Everything is published under a single editorial byline. That byline is a publishing identity for the site, not a claim about a named individual, and it does not carry professional credentials.

Corrections

Corrections are welcome. If something here is wrong, out of date, or attributed to the wrong source, email [email protected] with the page address and what it should say. Substantive corrections are made in the article itself rather than quietly dropped.

How this site is funded

This site currently runs no affiliate links, sponsored posts, display advertising or paid placements. If that changes, the disclosure page will say so.

Contact

Email: [email protected]
Site: cephclusterguide.com
Published by: CephClusterGuide Editorial

See also the privacy policy, the terms of use, and the editorial disclosure.