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mdadm

Introduction​

This cheat sheet provides a quick reference for some common mdadm (Multiple Device Administrator) commands and concepts. mdadm is a command-line utility used to manage software RAID (Redundant Array of Independent Disks) on Linux systems.

mdadm Concepts​

Creating RAID Arrays​

You can use mdadm to create RAID arrays.

  • Create a RAID 1 (mirrored) array:

    mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdX1 /dev/sdX2

  • Create a RAID 5 (striped with parity) array:

    mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sdX1 /dev/sdX2 /dev/sdX3

Managing RAID Arrays​

mdadm allows you to manage RAID arrays, including starting, stopping, and monitoring them.

  • Start a RAID array:

    mdadm --assemble /dev/md0

  • Stop a RAID array:

    mdadm --stop /dev/md0

  • Monitor RAID array status:

    mdadm --detail /dev/md0

Adding and Removing Drives​

You can add or remove drives from a RAID array.

  • Add a drive to a RAID array:

    mdadm --add /dev/md0 /dev/sdX3

  • Remove a drive from a RAID array:

    mdadm --remove /dev/md0 /dev/sdX3

Managing Failures​

mdadm can handle drive failures and rebuild RAID arrays.

  • Mark a drive as failed:

    mdadm --fail /dev/md0 /dev/sdX2

  • Remove a failed drive from the array:

    mdadm --remove /dev/md0 /dev/sdX2

  • Replace a failed drive with a new one:

    mdadm --replace /dev/md0 /dev/sdX2 /dev/sdX4

mdadm Command-Line​

  • Create a RAID 1 (mirrored) array:

    mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdX1 /dev/sdX2

  • Start a RAID array:

    mdadm --assemble /dev/md0

  • Stop a RAID array:

    mdadm --stop /dev/md0

  • Monitor RAID array status:

    mdadm --detail /dev/md0

  • Add a drive to a RAID array:

    mdadm --add /dev/md0 /dev/sdX3

  • Remove a drive from a RAID array:

    mdadm --remove /dev/md0 /dev/sdX3

  • Mark a drive as failed:

    mdadm --fail /dev/md0 /dev/sdX2

  • Remove a failed drive from the array:

    mdadm --remove /dev/md0 /dev/sdX2

  • Replace a failed drive with a new one:

    mdadm --replace /dev/md0 /dev/sdX2 /dev/sdX4

Conclusion​

This cheat sheet covers some common mdadm (Multiple Device Administrator) commands and concepts. mdadm is a powerful tool for managing software RAID arrays on Linux systems, providing redundancy and fault tolerance for data storage; refer to the official mdadm documentation for more in-depth information and advanced usage.