Software RAID on linux with mdadmCampus-Booster ID: 38503

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Software RAID

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Software RAID

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Create a loop device: to use RAID without additional disk

Know all differents RAID levels: choose the level for your need

Install and configure RAID software: when we had no hardware solution

Monitoring RAID devices: to be alerted of arrays problem

By completing this course, you will:

Software RAID

Course objectives

Loop devices: know and manipulate loop devices

System preparation: Configure the linux kernel and disks to use RAID

mdadm installation: the software RAID solution

RAID implementation: increase performance and implement fault tolerance

Monitoring and maintenance: Change disk or be aware of any problems

Software RAID

Course’s plan:

Course topics

Loop Devices

Introduction to Loop Devices

Software RAID

PreviewLoop devices

Here are chapters we will talk about:

Loop devices presentation

Example

PresentationLoop devices

Loopback device

Same operations as a real disk, example:

Can be bound to a file

File Virtual disk

Become /dev/loop[0-7]

fdisk /dev/loop0fdisk /dev/loop0

mkfs.ext3 /dev/loop0mkfs.ext3 /dev/loop0

ExampleLoop devices

Creation of a 10Mo file

Bind /dev/loop0 device to image.loop

Unbind:

dd if=/dev/zero of=image.loop bs=1024k count=10dd if=/dev/zero of=image.loop bs=1024k count=10

losetup /dev/loop0 image.looplosetup /dev/loop0 image.loop

losetup –d /dev/loop0losetup –d /dev/loop0

Stop-and-thinkLoop devices

Do you have any questions ?

Introduction to RAID

Redundant Array of Independent Disks

Software RAID

PreviewRAID introduction

Here are the chapters we will see:

Introduction

Stripping

Mirroring

RAID 5

RAID 1+0

Abbreviation

RedundantArray ofIndependentDisks

Introduction Objective: using inexpensive disks

Disks aggregation: the OS only sees one logical disk.

Disks capacity addition (RAID 0, JBOD)

Enhanced performance (RAID 0, 5)

Fault tolerance (RAID 1, 5)

Increase capacity, performance, security (RAID 5)

Hardware and Software implementation

IMPORTANT: it's not a backup solution!

RAID introduction

Raid – Historique

1987, Berkeley University: birth of the first 5 Raid levels RAID (1-5)

Raid 0, 6, 7 and Jbod added after

Level 0 and Jbod without fault tolerance (no

redundancy)

RAID introduction

RAID 0 (Stripping)

RAID 0

Enhanced performance

No fault tolerance

RAID introduction

RAID 1 (mirroring)

Raid level 1 or Mirroring

Fault tolerance

Enhanced performance on data reading

Disadvantage: not very disk space efficient

2 Disks of 40Go = 1 Raid device of 40Go

RAID introduction

RAID 5

Raid level 5

Mix between reliability and performance

Read/Write Data on all disks

Parity check system

RAID introduction

RAID 1+0

Raid 1+ Raid 0

Need 4 Disks minimum

Mix Raid 0 performance with Raid 1 Reliability

RAID introduction

Stop-and-thinkRAID introduction

Do you have any questions ?

Software Raid Implementation

Software Raid installation on Linux

Software RAID

PreviewSoftware RAID implementation

These are the chapters that we will approach :

Kernel configuration

mdadm installation

Disks preparation

RAID device

Kernel configuration

Linux kernel must support Raid devices

1 Verify Raid support:

2 Reconfigure the kernel if needed:

Software RAID implementation

cat /boot/config-2.6.x | grep RAIDcat /boot/config-2.6.x | grep RAID

mdadm installation

mdadm: Tool to manage raid devices

Install from sources:

http://neil.brown.name/blog/mdadm

Mandriva: urpmi mdadm

Software RAID implementation

Disks preparation

Partitions need to support raid

1 disk = only 1 partition

Warning: All data will be lost !

1 Launch fdisk or any other partition manager of your choice

2 Create a partition for the entire disk

3 Modify partition type to type FD (Linux RAID autodetect)

Software RAID implementation

fdisk /dev/hdbfdisk /dev/hdb

Raid device

Raid device = Virtual partition

Represented by: /dev/md<x>

X is a number: 0 to 15

Example: /dev/md1

16 Raid partitions maximum

No partitioning required on raid device.

Software RAID implementation

Stop-and-thinkSoftware RAID implementation

Do you have any questions ?

Configuration and use of Software RAID

Implementation of different Raid types.

Software RAID

PreviewConfiguration and use of Software RAID

These are the chapters that we will approach :

The mdadm command

RAID 1 Implementation

RAID 5 Implementation

RAID 0+1 Implementation

The mdadm command

Only one command for all management: mdadm

--create <device>: Raid device to create (/dev/md1)

--level=<x>: Raid level (0,1,5,...)

--raid-devices=<x> <devices>: number of physical disks and their access path

Configuration of Software RAID

mdadm --create <device> --level=<x> \> --raid-devices=<x> <device1> <device2> ...

mdadm --create <device> --level=<x> \> --raid-devices=<x> <device1> <device2> ...

Raid 1 implementation

Data duplicated: writing synchronously on all disks

2 disks minimum

Creation of a Raid 1 device /dev/md0

Mirroring of /dev/sdb1 and /dev/sdc1

Configuration of Software RAID

mdadm --create /dev/md0 --level=1 \> --raid-devices=2 /dev/sdb1 /dev/sdc1

mdadm --create /dev/md0 --level=1 \> --raid-devices=2 /dev/sdb1 /dev/sdc1

Raid 5 implementation

Fault tolerance and performance

3 disks minimum

Configuration of Software RAID

mdadm --create /dev/md1 --level=5 \> --raid-devices=3 /dev/sdb1 /dev/sdc1 /dev/sdd1 \> --spare-devices=1 /dev/sde1

mdadm --create /dev/md1 --level=5 \> --raid-devices=3 /dev/sdb1 /dev/sdc1 /dev/sdd1 \> --spare-devices=1 /dev/sde1

Raid 1+0 implementation Raid 1 + Raid 0

First we create two RAID 1

Configuration of Software RAID

mdadm --create /dev/md1 --level=1 \> --raid-devices=2 /dev/sdd1 /dev/sde1

mdadm --create /dev/md1 --level=1 \> --raid-devices=2 /dev/sdd1 /dev/sde1

mdadm --create /dev/md2 --level=0 \> --raid-devices=2 /dev/md0 /dev/md1

mdadm --create /dev/md2 --level=0 \> --raid-devices=2 /dev/md0 /dev/md1

mdadm --create /dev/md0 --level=1 \> --raid-devices=2 /dev/sdb1 /dev/sdc1

mdadm --create /dev/md0 --level=1 \> --raid-devices=2 /dev/sdb1 /dev/sdc1

And then the RAID 0 from the two RAID 1 sets

Stop-and-thinkConfiguration of Software RAID

Do you have any questions ?

Maintenance and monitoring

Maintenance and monitoring of Raid devices

Software RAID

PreviewMaintenance and monitoring

These are the chapters that we will approach :

Simulate a faulty disk

Hot add / remove

Monitoring your arrays

Simulate a faulty disk Hot add and remove of disk

Simulate a faulty disk:

See the changes:

1

2

Maintenance and monitoring

mdadm /dev/md0 -f /dev/sdc1mdadm /dev/md0 -f /dev/sdc1

mdadm --detail /dev/md0[ ? ] Number Major Minor RaidDevice State0 8 17 0 active sync /dev/sdb11 8 49 1 active sync /dev/sdd12 8 33 - faulty /dev/sdc1

mdadm --detail /dev/md0[ ? ] Number Major Minor RaidDevice State0 8 17 0 active sync /dev/sdb11 8 49 1 active sync /dev/sdd12 8 33 - faulty /dev/sdc1

Hot add / remove

Hot add and remove of disk

Remove /dev/sdc1

Add the spare disk /dev/sde1

3

4

Maintenance and monitoring

mdadm /dev/md0 -r /dev/sdc1mdadm /dev/md0 -r /dev/sdc1

mdadm /dev/md0 -a /dev/sde1mdadm /dev/md0 -a /dev/sde1

Monitoring your arrays

Get mail alerts about your RAID array state:

Maintenance and monitoring

mdadm -F --scan -f --delay 30 --pid-file \ > /var/run/mdadm.pid -m labo-linux@supinfo.com

mdadm -F --scan -f --delay 30 --pid-file \ > /var/run/mdadm.pid -m labo-linux@supinfo.com

Stop-and-thinkMaintenance and monitoring

Do you have any questions ?

RAID levelsRAID levels

Mdadm commandMdadm

command

RAID maintenance & monitoring

RAID maintenance & monitoring

Course summary

Loop devicesLoop devices

Software RAID

Congratulations

You have successfully completed the SUPINFO course

Software Raid

The end