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Archive for November, 2008

mdadm Cheatsheet

November 4th, 2008 No comments

Scan a system for RAID arrays and save findings so the array reappears across reboots:

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# mdadm --detail --scan && /etc/mdadm/mdadm.conf

Create a RAID5 array out of sdm1, sdj1, and a missing disk (all partitioned with raid-autodetect partitions)

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# mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sd[mj]1 missing

Create a RAID1 array

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# mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sd[ts]1

Remove a RAID array

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# mdadm --stop /dev/md1
# mdadm --zero-superblock /dev/sd[ts]1

Replace a failed drive that has been removed from the system

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# mdadm /dev/md3  --add /dev/sdc1 --remove detached

Add a new drive to an array, and remove an existing drive at the same time

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# mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1

Add a drive to a RAID 5 array, growing the array size

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# mdadm --add /dev/md1 /dev/sdm1
# mdadm --grow /dev/md1 --raid-devices=4

Fixing an incorrect /dev/md number (ie /dev/md127)

1. Remove any extra parameters for the array except for UUID in /etc/mdadm/mdadm.conf. Ex.

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#ARRAY /dev/md1 level=raid1 num-devices=2 metadata=1.2 UUID=839813e7:050e5af1:e20dc941:1860a6ae
ARRAY /dev/md1 UUID=839813e7:050e5af1:e20dc941:1860a6ae

2. Then rebuild the initramfs

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sudo update-initramfs -u
Categories: cheatsheet, file systems