Overview

An Overview of Software-RAID

This area of the wiki is based on "The Software RAID HowTo" by Jakob OEstergaard jakob@unthought.net and Emilio Bueso bueso@vives.org

This HOWTO describes how to use Software RAID under Linux. It addresses a specific version of the Software RAID layer, namely the 0.90 RAID layer currently maintained by Neil Brown. This is the RAID layer that is the standard in Linux-2.6 and Linux-2.4, and it is the version that is also used by Linux-2.2 kernels shipped from some vendors. The 0.90 RAID support is available as patches to Linux-2.0 and Linux-2.2, and is by many considered far more stable that the older RAID support already in those kernels.

 1. Introduction
    1.1 Disclaimer
    1.2 What is RAID?
    1.3 Terms
    1.4 The RAID levels
    1.5 Requirements

 2. Why RAID?
    2.1 Device and filesystem support
    2.2 Performance
    2.3 Swapping on RAID
    2.4 Why mdadm?

 3. Devices
    3.1 Spare disks
    3.2 Faulty disks

 4. Hardware issues
    4.1 IDE Configuration
    4.2 Hot Swap
       4.2.1 Hot-swapping IDE drives
       4.2.2 Hot-swapping SCSI drives
       4.2.3 Hot-swapping with SCA

 5. RAID setup
    5.1 General setup
    5.2 Downloading and installing the RAID tools
    5.3 Downloading and installing mdadm
    5.4 Linear mode
    5.5 RAID-0
    5.6 RAID-1
    5.7 RAID-4
    5.8 RAID-5
    5.9 The Persistent Superblock
    5.10 Chunk sizes
       5.10.1 RAID-0
       5.10.2 RAID-0 with ext2
       5.10.3 RAID-1
       5.10.4 RAID-4
       5.10.5 RAID-5
    5.11 Options for mke2fs

 6. Detecting, querying and testing
    6.1 Detecting a drive failure
    6.2 Querying the arrays status
    6.3 Simulating a drive failure
       6.3.1 Force-fail by hardware
       6.3.2 Force-fail by software
    6.4 Simulating data corruption
    6.5 Monitoring RAID arrays

 7. Tweaking, tuning and troubleshooting
    7.1 raid-level and raidtab
    7.2 Autodetection
    7.3 Booting on RAID
    7.4 Root filesystem on RAID
       7.4.1 Method 1
       7.4.2 Method 2
    7.5 Making the system boot on RAID
       7.5.1 Booting with RAID as module
       7.5.2 Modular RAID on Debian GNU/Linux after move to RAID
    7.6 Converting a non-RAID RedHat System to run on Software RAID
       7.6.1 Introduction
       7.6.2 Scope
       7.6.3 Pre-conversion example system
       7.6.4 Step-1 - boot rescue cd/floppy
       7.6.5 Step-2 - create a /etc/raidtab file
       7.6.6 Step-3 - create the md devices
       7.6.7 Step-4 - unmount filesystems
       7.6.8 Step-5 - start raid devices
       7.6.9 Step-6 - remount filesystems
       7.6.10 Step-7 - change root
       7.6.11 Step-8 - edit config files
       7.6.12 Step-9 - run LILO
       7.6.13 Step-10 - change partition types
       7.6.14 Step-11 - resize filesystem
       7.6.15 Step-12 - checklist
       7.6.16 Step-13 - reboot
    7.7 Sharing spare disks between different arrays
    7.8 Pitfalls

 8. Reconstruction
    8.1 Recovery from a multiple disk failure

 9. Performance
    9.1 RAID-0
    9.2 RAID-0 with TCQ
    9.3 RAID-5
    9.4 RAID-10
    9.5 Fresh benchmarking tools

 10. Related tools
    10.1 RAID resizing and conversion
    10.2 Backup

 11. Partitioning RAID / LVM on RAID
    11.1 Partitioning RAID devices
    11.2 LVM on RAID

 12. Credits
 13. Changelog
    13.1 Version 1.1