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48 lines
1.6 KiB
Markdown
48 lines
1.6 KiB
Markdown
# MDADM
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`mdadm` is a utility to create and manage raid devices.
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## Usage
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### Get information about a raid
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To get an info for a running raid (assuming it is `/dev/md0`) run
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`mdadm -D /dev/md0`.
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### Add disk/partition to raid device
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You can add a disk or partition to a raid device by running the following.
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It is assumed you are adding a partition called `/dev/sdd1` but it could also
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be a whole drive and the mdadm drive is called `/dev/md0`.
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`mdadm --add /dev/md0 /dev/sdd1`
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### Raid 1
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Raid 1 creates a mirror with even amount of drives.
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#### Create raid 1 device
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You can create a Raid 1 device with
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`mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda /dev/sdb`
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where `sda` and `sdb` are the disks you want to include in your raid.
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You can increase the number of raid devices, but they have to be at least 2.
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If it is an uneven amount of disks in the raid, a disk will act as a spare disk.
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#### Convert raid 1 to raid 5
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Assuming the raid device is called `/dev/md0`.
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All other drives are part of the `md0` raid device.
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- Remove all drives but 2 by running `mdadm /dev/md0 --fail /dev/sda1` and
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`mdadm /dev/md0 --remove /dev/sda1` where `sda1` is the drive to remove
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- Make sure your raid 1 array has only 2 active drives by running
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`mdadm --grow /dev/md0 -n 2`
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- Now convert your raid 1 to a raid 5 device with `mdadm --grow /dev/md0 -l5`
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- Add the disks you removed back to the raid with
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`mdadm /dev/md0 --add /dev/sda1`
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- Finally grow the active drive number to your needs (in this example 4)
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`mdadm --grow /dev/md0 -n4`
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- `mdadm` now reshapes the raid. You can monitor it by running
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`watch cat /proc/mdstat`
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