8 min to read

Understanding Ceph: Comprehensive Guide to Distributed Storage Architecture

An in-depth exploration of Ceph's architecture, components, and operational best practices for modern data centers

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Overview

Today, we’ll explore the fundamental concepts, architecture, key features, and operational considerations of Ceph distributed storage system.

Ceph is an open-source distributed storage system that uniquely supports Object, Block, and File storage within a single unified system. It provides powerful capabilities including High Availability, horizontal Scalability, and Self-Healing, making it widely adopted in cloud environments and large-scale data centers.

This article will cover Ceph’s major architectural components (MON, MGR, OSD, MDS, RGW), the CRUSH algorithm for effective data placement, performance optimization, and operational best practices.

In the next article, we’ll dive deeper into Ceph-Kubernetes integration (Rook-Ceph) and operational automation.


What is Ceph?

Ceph is a distributed storage system that clusters multiple storage devices to appear as a single unified storage system.

It implements object storage on a distributed cluster, providing storage interfaces at object, block, and file levels. The key advantage is that it provides object storage, block storage, and file system capabilities all in one solution.

Ceph offers complete distributed processing without SPOF (Single Point of Failure) and can scale up to exabyte levels. To configure a Ceph Storage Cluster, you need at least one Ceph Monitor, Ceph Manager, and Ceph OSD (Object Storage Daemon). If you want to use Ceph File System clients, you also need a Ceph Metadata Server.


Key Advantages of Ceph


High Availability & Zero Downtime


Horizontal Scalability


Multiple Storage Interface Support


Open Source Foundation


Key Disadvantages of Ceph


High Hardware Requirements


Complex Configuration


Recovery Speed


Ceph Architecture and Daemons


Component Overview

Each daemon plays the following roles in the Ceph ecosystem:


Monitors (MON)


Managers (MGR)


Ceph OSDs


MDSs (Metadata Servers)


Ceph Object Gateway (RGW)


Ceph Client Interfaces

Ceph provides various service interfaces for external data management:


RADOS (Ceph Storage Cluster)


RADOS Block Device (RBD)


Ceph Object Gateway (RADOS Gateway)


Ceph File System (CephFS)


Placement Groups (PGs)

Storing and managing millions of objects individually in a cluster is resource-intensive. Therefore, Ceph uses Placement Groups (PGs) to manage numerous objects more efficiently.


Key Concepts:


Pool Types

Ceph supports data durability through two primary pool types:


Replicated Pool


Erasure Coded Pool


CRUSH Algorithm (Controlled Replication Under Scalable Hashing)

CRUSH Algorithm


Core Algorithm for Distributed Data Placement

Key Features:


CRUSH Operation Process:

  1. Object Hashing: Converts objects to hash values
  2. PG Mapping: Maps to appropriate Placement Groups
  3. OSD Placement: Uses CRUSH algorithm to place PGs on suitable OSDs
  4. Failure Recovery: Updates CRUSH Map and performs automatic recovery

CRUSH is the core technology that maximizes distributed storage efficiency without traditional centralized metadata servers.


Performance Tuning and Best Practices


Core Optimization Elements

Increase OSD Count

SSD-based WAL/DB Configuration

Network Optimization

CRUSH Map Optimization

Erasure Coding Optimization


Ceph Use Cases


OpenStack Integration


Kubernetes Persistent Storage


Large-Scale Deployments


Cephadm vs ceph-ansible Comparison

Feature Cephadm ceph-ansible
Deployment Method Container-based Package-based
Difficulty Easy Relatively Complex
Upgrades Rolling Upgrade Support Manual Upgrade Required
Monitoring Dashboard Included Manual Grafana Setup
Recommended For New Deployments Existing Environment Maintenance


Production Troubleshooting Scenarios

Issue Type Cause Resolution Method
OSD Flapping Disk performance degradation, Network latency Analyze OSD logs, Replace or tune hardware
MON Quorum Instability Insufficient MON count, Network partition Maintain 3+ MONs, Check network connectivity
Cluster Full Status Poor capacity management Configure Pool quotas, Adjust data policies
Scrub Errors Data inconsistency, Disk errors Perform manual repair, Replace faulty disks


Monitoring and Maintenance


Essential Monitoring Metrics


Regular Maintenance Tasks


Conclusion

Throughout this article, we’ve explored Ceph’s fundamental concepts, architectural components, major daemon roles, advantages and disadvantages, and essential information for production operations.

Ceph is not just a simple storage system, but a powerful distributed storage solution that provides object, block, and file storage on a single platform. It has established itself as a robust storage backend with flexibility, scalability, and high availability in OpenStack, Kubernetes, and large-scale data storage environments.

However, Ceph is not a “set-and-forget” solution. It requires operational expertise from initial design through performance tuning, continuous monitoring, and incident response procedures.

The content covered today serves as a practical guide for both newcomers to Ceph and engineers building operational experience with the platform.


Key Takeaways:


References