add mdadm

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Malin Freeborn 2022-01-14 12:32:40 +01:00
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# RAID5
You will need 4 disks and the `mdadm` package.
The total size will be equal to the disks x 3, because one will be used for redundancy.
> sudo mdadm --create --verbose /dev/*md127* --level=5 --raid-devices=*4* */dev/sdb /dev/sdc /dev/sdd /dev/sde*
Note the variable parts:
- The name of the device could be `/dev/md12` or whatever
- The number of devices could be larger, but must be at least 4 for raid 5
- We end by listing all devices in the new `md` device.
Now look at how the raid status:
> cat /proc/mdstat
This will increase until the entire thing is fine.
Check the health of your `mdadm` array:
> sudo mdadm --detail /dev/md127
You should see `State : clean`. If you see it is `degraded`, then a disk has broken.
## Replacing a Disk
First, prepare the disk with both a gpt partition table, and a partition:
> sudo parted --script /dev/sdb mklabel gpt mkpart primary 1MiB -2048s
Add the appropriate file system to it, e.g.:
> sudo mkfs.ext4 /dev/sdb1
Then finally, add the disk:
> sudo mdadm --add /dev/md127 /dev/sdb1