Mastering Ceph E-Book

Nick Fisk

• Herausgeber: Packt Publishing
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 265

Veröffentlichungsjahr: 2017

Beschreibung

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.

Leseprobe

Title Page

Mastering Ceph

Redefine your storage system

Nick Fisk

BIRMINGHAM - MUMBAI

Copyright

Mastering Ceph

Copyright © 2017 Packt Publishing

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First published: May 2017

Production reference: 1260517

Published by Packt Publishing Ltd.

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Credits

Author

Nick Fisk

Copy Editor

Dipti Mankame

Reviewer

Vladimir Franciz S. Blando

Project Coordinator

Judie Jose

Commissioning Editor

Pratik Shah

Proofreader

Safis Editing

Acquisition Editor

Meeta Rajani

Indexer

Rekha Nair

Content Development Editor

Juliana Nair

Graphics

Kirk D'Penha

Technical Editor

Gaurav Suri

Production Coordinator

Aparna Bhagat

About the Author

Nick Fisk is an IT specialist with a strong history in enterprise storage. Having worked in a variety of roles throughout his career, he has encountered a wide variety of technologies. In 2012, Nick was given the opportunity to focus more toward open source technologies, and this is when his first exposure to Ceph happened. Having seen the potential of Ceph as a storage platform and the benefits of moving away from the traditional closed-stack storage platforms, Nick pursued Ceph with a keen interest.

Throughout the following years, his experience with Ceph increased with the deployment of several clusters and enabled him to spend time in the Ceph community, helping others and improving certain areas of Ceph.

I would firstly like to thank my wife for allowing me to dedicate time to writing this book and to Juliana Nair for supporting me through the writing process.I would also like to especially thank Tarquin Dunn for the continual support and encouragement he has given me from the initial adoption of Ceph as a storage platform. His support has enabled me to both learn and contribute to this amazing open source project.

About the Reviewer

Vladimir Franciz S. Blando is a seasoned IT professional with 18 years' experience of Linux systems administration, including architecture, design, installation, configuration, and maintenance, working on both bare-metal and virtualized environments. He is well versed in Amazon Web Services, OpenStack cloud, Ceph storage, and other cloud technologies.

I would like to thank Morphlabs for giving me the opportunity to work on various cloud technologies, especially OpenStack and Ceph, and for supporting me all throughout.

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Table of Contents

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Downloading the color images of this book

Errata

Piracy

Questions

Planning for Ceph

What is Ceph?

How Ceph works?

Ceph use cases

Replacing your storage array with Ceph

Performance

Reliability

The use of commodity hardware

Specific use cases

OpenStack- or KVM-based virtualization

Large bulk block storage

Object storage

Object storage with custom application

Distributed filesystem - web farm

Distributed filesystem -SMB file server replacement

Infrastructure design

SSDs

Consumer

Prosumer

Enterprise SSDs

Enterprise -read intensive

Enterprise - general usage

Enterprise -write intensive

Memory

CPU

Disks

Networking

10G networking requirement

Network design

OSD node sizes

Failure domains

Price

Power supplies

How to plan a successful Ceph implementation

Understanding your requirements and how it relates to Ceph

Defining goals so that you can gauge if the project is a success

Choosing your hardware

Training yourself and your team to use Ceph

Running PoC to determine if Ceph has met the requirements

Following best practices to deploy your cluster

Defininga change management process

Creating a backup and recovery plan

Summary

Deploying Ceph

Preparing your environment with Vagrant and VirtualBox

System requirements

Obtaining and installing VirtualBox

Setting up Vagrant

The ceph-deploy tool

Orchestration

Ansible

Installing Ansible

Creating your inventoryfile

Variables

Testing

A very simple playbook

Adding the Ceph Ansible modules

Deploying a test cluster with Ansible

Change and configuration management

Summary

BlueStore

What is BlueStore?

Why was it needed?

Ceph's requirements

Filestore limitations

Why is BlueStore the solution?

How BlueStore works

RocksDB

Deferred writes

BlueFS

How to use BlueStore

Upgrading an OSD in your test cluster

Summary

Erasure Coding for Better Storage Efficiency

What is erasurecoding?

K+M

How does erasure coding work in Ceph?

Algorithms and profiles

Jerasure

ISA

LRC

SHEC

Where can I use erasure coding?

Creating an erasure-coded pool

Overwrites on erasure code pools with Kraken

Demonstration

Troubleshooting the 2147483647 error

Reproducing the problem

Summary

Developing with Librados

What is librados?

How to use librados?

Example librados application

Example of the librados application with atomic operations

Example of the librados application that uses watchers and notifiers

Summary

Distributed Computation with Ceph RADOS Classes

Example applications and the benefits of using RADOS classes

Writing a simple RADOS class in Lua

Writing a RADOS class that simulates distributed computing

Preparing the build environment

RADOS class

Client librados applications

Calculating MD5 on the client

Calculating MD5 on the OSD via RADOS class

Testing

RADOS class caveats

Summary

Monitoring Ceph

Why it is important to monitor Ceph

What should be monitored

Ceph health

Operating system and hardware

Smart stats

Network

Performance counters

PG states -the good, the bad, and the ugly

The good

The active state

The clean state

Scrubbing and deep scrubbing

The bad

The inconsistent state

The backfilling, backfill_wait, recovering, recovery_wait states

The degraded state

Remapped

The ugly

The incomplete state

The down state

The backfill_toofull state

Monitoring Ceph with collectd

Graphite

Grafana

collectd

Deploying collectd with Ansible

Sample Graphite queries for Ceph

Number of Up and In OSDs

Showing most deviant OSD usage

Total number of IOPs across all OSDs

Total MBps across all OSDs

Cluster capacity and usage

Average latency

Custom Ceph collectd plugins

Summary

Tiering with Ceph

Tiering versus caching

How Cephs tiering functionality works

What is a bloom filter

Tiering modes

Writeback

Forward

Read-forward

Proxy

Read-proxy

Uses cases

Creating tiers in Ceph

Tuning tiering

Flushing and eviction

Promotions

Promotion throttling

Monitoring parameters

Tiering with erasure-coded pools

Alternative caching mechanisms

Summary

Tuning Ceph

Latency

Benchmarking

Benchmarking tools

Fio

Sysbench

Ping

iPerf

Network benchmarking

Disk benchmarking

RADOS benchmarking

RBD benchmarking

Recommended tunings

CPU

Filestore

VFS cache pressure

WBThrottle and/or nr_requests

Filestore queue throttling

filestore_queue_low_threshhold

filestore_queue_high_threshhold

filestore_expected_throughput_ops

filestore_queue_high_delay_multiple

filestore_queue_max_delay_multiple

PG Splitting

Scrubbing

OP priorities

The Network

General system tuning

Kernel RBD

Queue Depth

ReadAhead

PG distributions

Summary

Troubleshooting

Repairing inconsistent objects

Full OSDs

Ceph logging

Slow performance

Causes

Increased client workload

Down OSDs

Recovery and backfilling

Scrubbing

Snaptrimming

Hardware or driver issues

Monitoring

iostat

htop

atop

Diagnostics

Extremely slow performance or no IO

Flapping OSDs

Jumbo frames

Failing disks

Slow OSDs

Investigating PGs in a down state

Large monitor databases

Summary

Disaster Recovery

What is a disaster?

Avoiding data loss

What can cause an outage or data loss?

RBD mirroring

The journal

The rbd-mirror daemon

Configuring RBD mirroring

Performing RBD failover

RBD recovery

Lost objects and inactive PGs

Recovering from a complete monitor failure

Using the Cephs object store tool

Investigating asserts

Example assert

Summary

Preface

Ceph, a unified, highly resilient, distributed storage system that provides block, object, and file access, has enjoyed a surge in popularity over the last few years. Due to being open source, Ceph has enjoyed rapid adoption both from developers and end users alike, with several well-known corporations being involved in the project. With every new release, the scale of its performance and feature set continues to grow, further enhancing Ceph's status.

With the current ever-increasing data storage requirements and challenges faced by legacy RAID-based systems, Ceph is well placed to offer an answer to these problems. As the world moves forward adopting new cloud technologies and object-based storage, Ceph is ready and waiting to be the driving force as part of the new era of storage technologies.

In this book, we will cover a wide variety of topics, from installing and managing a Ceph cluster to how to recover from disasters, should you ever find yourself in that situation. For those that have interest in getting their applications to talk directly to Ceph, this book will also show you how to develop applications that make use of Ceph's libraries and even how to perform distributed computing by inserting your own code into Ceph. By the end of this book, you will be well on your way to mastering Ceph.

What this book covers

Chapter 1, Planning for Ceph, covers the basics of how Ceph works, its basic architecture, and what some good use cases are. It also discusses the steps that one should take to plan before implementing Ceph, including design goals, proof of concept, and infrastructure design.

Chapter 2, Deploying Ceph, is a no-nonsense step-by-step instructional chapter on how to set up a Ceph cluster. This chapter covers the ceph-deploy tool for testing and goes onto covering Ansible. A section on change management is also included, and it explains how this is essential for the stability of large Ceph clusters. This chapter also serves the purpose of providing you with a common platform you can use for examples later in the book.

Chapter 3, BlueStore, explains that Ceph has to be able to provide atomic operations around data and metadata and how filestore was built to provide these guarantees on top of standard filesystems. We will also cover the problems around this approach. The chapter then introduces BlueStore and explains how it works and the problems that it solves. This will include the components and how they interact with different types of storage devices. We will also have an overview of key-value stores, including RocksDB, which is used by BlueStore. Some of the BlueStore settings and how they interact with different hardware configurations will be discussed.

Chapter 4, Erasure Coding for Better Storage Efficiency, covers how erasure coding works and how it's implemented in Ceph, including explanations of RADOS pool parameters and erasure coding profiles. A reference to the changes in the Kraken release will highlight the possibility of append-overwrites to erasure pools, which will allow RBDs to directly function on erasure-coded pools. Performance considerations will also be explained. This will include references to BlueStore, as it is required for sufficient performance. Finally, we have step-by-step instructions on actually setting up erasure coding on a pool, which can be used as a mechanical reference for sysadmins.

Chapter 5, Developing with Librados, explains how Librados is used to build applications that can interact directly with a Ceph cluster. It then moves onto several different examples of using Librados in different languages to give you an idea of how it can be used, including atomic transactions.

Chapter 6, Distributed Computation with Ceph RADOS Classes, discusses the benefits of moving processing directly into the OSD to effectively perform distributed computing. It then covers how to get started with RADOS classes by building simple ones with Lua. It then covers how to build your own C++ RADOS class into the Ceph source tree and conduct benchmarks against performing processing on the client versus the OSD.

Chapter 7, Monitoring Ceph, starts with a description of why monitoring is important and discusses the difference between alerting and monitoring. The chapter will then cover how to obtain performance counters from all the Ceph components and explain what some of the key counters mean and how to convert them into usable values.

Chapter 8, Tiering with Ceph, explains how RADOS tiering works in Ceph, where it should be used, and its pitfalls. It takes you step-by-step through configuring tiering on a Ceph cluster and finally covers the tuning options to extract the best performance for tiering. An example using Graphite will demonstrate the value of being able to manipulate captured data to provide more meaningful output in graph form.

Chapter 9, Tuning Ceph, starts with a brief overview of how to tune Ceph and the operating system. It also covers basic concepts of avoiding trying to tune something that is not a bottleneck. It will also cover the areas that you may wish to tune and establish how to gauge the success of tuning attempts. Finally, it will show you how to benchmark Ceph and take baseline measurements so that any results achieved are meaningful. We'll discuss different tools and how benchmarks might relate to real-life performance.

Chapter 10, Troubleshooting, explains how although Ceph is largely autonomous in taking care of itself and recovering from failure scenarios, in some cases, human intervention is required. We'll look at common errors and failure scenarios and how to bring Ceph back to full health by troubleshooting them.

Chapter 11, Disaster Recovery, covers situations when Ceph is in such a state that there is a complete loss of service or data loss has occurred. Less familiar recovery techniques are required to restore access to the cluster and, hopefully, recover data. This chapter arms you with the knowledge to attempt recovery in these scenarios.

What you need for this book

This book assumes medium-level knowledge of Linux operating systems and basic knowledge of storage technologies and networking. Although the book will go through a simple multi-node setup of a Ceph cluster, it is advisable that you have some prior experience of using Ceph. Although the book uses VirtualBox, feel free to use any other lab environment, such as VMware Workstation.

This book requires that you have enough resources to run the whole Ceph lab environment. The minimum hardware or virtual requirements are as follows:

CPU: 2 cores

Memory: 8 GB RAM

Disk space: 40 GB

You will need the following software:

VirtualBox

Vagrant

Internet connectivity is required to install the packages that are part of the examples in each chapter.

Who this book is for

To make use of the content of this book, basic prior knowledge of Ceph is expected. If you feel you don't have that knowledge, it is always possible to catch up with the basics by having a quick read of the major components from the official Ceph documentation, http://docs.ceph.com/docs/master/. This book is essentially intended for Ceph cluster administrators. If you are already running a Ceph cluster, this book can help you to gain a better understanding.

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Planning for Ceph

The first chapter of this book covers all the areas you need to consider when looking to deploy a Ceph cluster from initial planning stages to hardware choices. Topics covered in this chapter are as follows:

What Ceph is and how it works

Good use cases for Ceph and important considerations

Advice and best practices on infrastructure design

Ideas around planning a Ceph project

What is Ceph?

Ceph is an open source, distributed, scale-out, software-defined storage (SDS) system, which can provide block, object, and file storage. Through the use of the Controlled Replication Under Scalable Hashing (CRUSH) algorithm, Ceph eliminates the need for centralized metadata and can distribute the load across all the nodes in the cluster. Since CRUSH is an algorithm, data placement is calculated rather than being based on table lookups and can scale to hundreds of petabytes without the risk of bottlenecks and the associated single points of failure. Clients also form direct connections with the server storing the requested data and so their is no centralised bottleneck in the data path.

Ceph provides the three main types of storage, being block via RADOS Block Devices (RBD), file via Ceph Filesystem (CephFS), and object via the Reliable Autonomous Distributed Object Store (RADOS) gateway, which provides Simple Storage Service (S3) and Swift compatible storage.

Ceph is a pure SDS solution and as such means that you are free to run it on commodity hardware as long as it provides the correct guarantees around data consistency. More information on the recommended types of hardware can be found later on in this chapter. This is a major development in the storage industry which has typically suffered from strict vendor lock-in. Although there have been numerous open source projects to provide storage services. Very few of them have been able to offer the scale and high resilience of Ceph, without requiring propriety hardware.

It should be noted that Ceph prefers consistency as per the CAP theorem and will try at all costs to make protecting your data the biggest priority over availability in the event of a partition.

How Ceph works?

The core storage layer in Ceph is RADOS, which provides, as the name suggests, an object store on which the higher level storage protocols are built and distributed. The RADOS layer in Ceph comprises a number of OSDs. Each OSD is completely independent and forms peer-to-peer relationships to form a cluster. Each OSD is typically mapped to a single physical disk via a basic host bus adapter (HBA) in contrast to the traditional approach of presenting a number of disks via a RedundantArray of IndependentDisks (RAID) controller to the OS.

The other key component in a Ceph cluster are the monitors; these are responsible for forming cluster quorum via the use of Paxos. By forming quorum the monitors can be sure that are in a state where they are allowed to make authoritative decisions for the cluster and avoid split brain scenarios. The monitors are not directly involved in the data path and do not have the same performance requirements as OSDs. They are mainly used to provide a known cluster state including membership, configuration, and statistics via the use of various cluster maps. These cluster maps are used by both Ceph cluster components and clients to describe the cluster topology and enable data to be safely stored in the right location.

Due to the scale that Ceph is intended to be operated at, one can appreciate that tracking the state and placement of every single object in the cluster would become computationally very expensive. Ceph solves this problem using CRUSH to place the objects into groups of objects named placement groups (PGs). This reduces the need to track millions of objects to a much more manageable number in the thousands range.

Librados is a Ceph library that can be used to build applications that interact directly with the RADOS cluster to store and retrieve objects.

For more information on how the internals of Ceph work, it would be strongly recommended to read the official Ceph documentation and also the thesis written by Sage Weil, the creator and primary architect of Ceph.

Ceph use cases

Before jumping into a specific use case, let's cover some key points that should be understood and considered before thinking about deploying a Ceph cluster.

Replacing your storage array with Ceph

Ceph should not be compared with a traditional scale-up storage array. It is fundamentally different, and trying to shoehorn Ceph into that role using existing knowledge, infrastructure, and expectation will lead to disappointment. Ceph is Software Defined Storage (SDS) whose internal data movements operate over TCP/IP networking. This introduces several extra layers of technology and complexity compared with a SAS cable at the rear of a traditional storage array.

Performance

Due to Ceph's distributed approach, it can offer unrestrained performance compared with scale-up storage arrays, which typically have to funnel all I/O through a pair of controller heads. Although technology has constantly been providing new faster CPUs and faster network speeds, there is still a limit to the performance you can expect to achieve with just a pair of controllers. With recent advances in flash technology combined with new interfaces such as Non-volatile Memory Express (NVMe), the scale-out nature of Ceph provides a linear increase in CPU and network resource with every added OSD node.

Let us also consider where Ceph is not a good fit for performance, and this is mainly around use cases where extremely low latency is desired. For the very reason that enables Ceph to become a scale-out solution, it also means that low latency performance will suffer. The overhead of software and additional network hops means that latency will tend to be about double that of a traditional storage array and 10 times that of local storage. A thought should be given to selecting the best technology for given performance requirements. That said, a well-designed and tuned Ceph cluster should be able to meet performance requirements in all but the most extreme cases.

Reliability

Ceph is designed to provide a highly fault-tolerant storage system by the scale-out nature of its components. Although no individual component is highly available, when clustered together any component should be able to fail without causing an inability to service client requests. In fact, as your Ceph cluster grows, the failure of individual components should be expected and become part of normal operating conditions. However, Ceph's ability to provide a resilient cluster should not be an invitation to compromise on hardware or design choice. Doing so will likely lead to failure. There are several factors that Ceph assumes your hardware will meet, which are covered later in this chapter.

Unlike RAID where disk rebuilds with larger disks can now stretch into time periods measured in weeks, Ceph will often recover from single disk failures in a matter of hours. With the increasing trend of larger capacity disks, Ceph offers numerous advantages to both the reliability and degraded performance when compared with a traditional storage array.

The use of commodity hardware

Ceph is designed to be run on commodity hardware, which gives the ability to be able to design and build a cluster without the premium demanded by traditional tier 1 storage and server vendors. This can be both a blessing and a curse. Be able to choose your own hardware that allows you to build your Ceph infrastructure to exactly match your requirements. However, one thing branded hardware does offer is compatibility testing; it's not unknown for strange exotic firmware bugs to be discovered, which can cause very confusing symptoms. A thought should be applied to whether your IT teams have the time and skills to cope with any obscure issues that may crop up with untested hardware solutions.

The use of commodity hardware also protects against the traditional fork lift upgrade model, where the upgrade of a single component often requires the complete replacement of the whole storage array. With Ceph you can replace individual components in a very granular nature, and with automatic data balancing, lengthy data migration periods are avoided. The distributed nature of Ceph means that hardware replacement or upgrades can be done during working hours without effecting service availability.

Specific use cases

We will now cover some of the more common uses cases for Ceph and discuss some of the reasons behind them.

OpenStack- or KVM-based virtualization

Ceph is the perfect match to provide storage to an OpenStack environment. In fact, Ceph currently is the most popular choice. OpenStack Cinder