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mdadm --zero-superblock /dev/sda2
TODO: is this next step necessary or even possible (it was not in PTDC-361)
Finally remove the device:
mdadm --remove /dev/md1
Booting from an md RAID 1 device
...
When a RAID 1 md device is used for /boot, GRUB should be installed to both underlying devices, not to the md device. This is done using
dpkg-reconfigure grub-pc-grub
GRUB2 can be configured to include md support so can assemble the /boot md before loading initrd (or the kernel directly) but Blue Light accepts what the distro delivers.
...
/usr/share/mdadm/mkconf > /etc/mdadm/mdadm.conf
It is prudent to rebuild the initramfs after changing mdadm.conf:
update-initramfs -u
mdadm syntax table
In case mdadm --help and the mdam man page are not what is needed.
...
Mode | device before options | Options | Notes |
|---|---|---|---|
| --assemble | Y | bitmap, uuid, super-minor, name, config, scan, run, force, update, no-degraded | |
| --build | Y | ||
| --create | Y | ||
| --grow | N | ||
| --incremental | No options | ||
| --misc | N | ||
| --manage | Y | add, remove, fail, set-faulty, run, stop, readonly, readwrite | --manage may be omitted |
| --monitor | No device |
Troubleshooting
Degraded array report
The system my detect a problem with the array and drop an underlying device. This is normally reported by mail and by Nagios.
It can be confirmed and the excluded underlying device (partition) identified by cat /proc/mdstat
Defects in the physical device may be identified in kern.log and by smartctl -a /dev/sd<letter>
In case smartctl output shows extended tests are not being run (old build computers), update /etc/smarttd.conf from git and edit to suit.
In case no defects are found, there is no choice but to add the excluded underlying device back into the md device as documented under "Replacing an underlying device" above.
If defects are found, ensure the underlying device is not used again by zeroing its md superblock as documented under "Remove an underlying device (md device not in use)" above.
In one case (bafi), during boot an array was assembled from a defective underlying device and the good underlying device excluded.
initrd fails to assemble md devices
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- Overview: md man page
- mdadm man page
- mdadm.conf man page
- kernel.org WIKI: https://raid.wiki.kernel.org/index.php/RAID_setup
- Wikiversity (nicw nice summary): https://en.wikiversity.org/wiki/Linux/mdadm