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@ -5,12 +5,12 @@ For the rest of this entry `n` is the number of drives inside a raid device.
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## Usage
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## Usage
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### Get information about a raid
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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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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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`mdadm -D /dev/md0`.
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### Add disk/partition to raid device
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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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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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It is assumed you are adding a partition called `/dev/sdd1` but it could also
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@ -18,6 +18,24 @@ 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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`mdadm --add /dev/md0 /dev/sdd1`
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This will add the disk as spare to the existing raid.
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To make the disk active the raid needs to be grown as described in the
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[regarding article](#growing-raid-device).
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### Growing Raid Device
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Growing a raid device will increase its number of active drives.
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[Check the number of active drives](#get-information-about-a-raid).
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Then change and run the following command accordingly.
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```sh
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mdadm --grow --raid-disks=5 /dev/md0
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```
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`/dev/md0` is the raid device.
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`5` is the number of disks that should be active.
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For adding disks view the [previous section](#add-diskpartition-to-raid-device).
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### Raid 1
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### Raid 1
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Raid 1 creates a mirror with even amount of drives.
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Raid 1 creates a mirror with even amount of drives.
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@ -25,7 +43,7 @@ For `n=2` [raid 5](#raid-5) and raid 1 are basically the same.
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The space efficiency is `1/n` and the fault tolerance is `n-1` drive failure.
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The space efficiency is `1/n` and the fault tolerance is `n-1` drive failure.
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The read perfromance is `n` and the write performance `1`.
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The read perfromance is `n` and the write performance `1`.
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#### Create raid 1 device
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#### Create Raid 1 Device
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You can create a Raid 1 device with
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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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`mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda /dev/sdb`
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@ -33,7 +51,7 @@ 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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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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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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#### Convert Raid 1 to Raid 5
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Assuming the raid 1 device is called `/dev/md0`.
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Assuming the raid 1 device is called `/dev/md0`.
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All other drives are part of the `md0` raid device.
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All other drives are part of the `md0` raid device.
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