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@ -1,6 +1,7 @@
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# MDADM
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`mdadm` is a utility to create and manage raid devices.
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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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@ -21,6 +22,8 @@ be a whole drive and the mdadm drive is called `/dev/md0`.
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Raid 1 creates a mirror with even amount of drives.
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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 read perfromance is `n` and the write performance `1`.
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#### Create raid 1 device
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@ -52,7 +55,11 @@ Note that mostly raid 1 devices consisting of 2 drives should be converted to
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### Raid 5
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Raid 5 creates a raid device with distributed parity.
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For `n>1` drives with the same size it creates a raid device with the size `n-1`
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drives.
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For `n=2` raid 5 and [raid 1](#raid-1) are basically the same.
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Raid 5 creates a raid device with distributed parity and is set to have at least
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3 drives.
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The space efficiency is `1-(1/n)` and the fault tolerance is `1` drive failure.
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The read perfromance is `n` and the write performance `1/4` for single sector
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and `n-1` for full stripe.
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In the special case of 2 drives in a raid 5 it is functionally the same as
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[raid 1](#raid-1).
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