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mdadm: added raid 5

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tiyn 2023-03-22 15:49:17 +01:00
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wiki/linux/mdadm.md
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@ -1,6 +1,7 @@
# MDADM # MDADM
`mdadm` is a utility to create and manage raid devices. `mdadm` is a utility to create and manage raid devices.
For the rest of this entry `n` is the number of drives inside a raid device.
## Usage ## Usage
@ -21,6 +22,8 @@ be a whole drive and the mdadm drive is called `/dev/md0`.
Raid 1 creates a mirror with even amount of drives. Raid 1 creates a mirror with even amount of drives.
For `n=2` [raid 5](#raid-5) and raid 1 are basically the same. For `n=2` [raid 5](#raid-5) and raid 1 are basically the same.
The space efficiency is `1/n` and the fault tolerance is `n-1` drive failure.
The read perfromance is `n` and the write performance `1`.
#### Create raid 1 device #### Create raid 1 device
@ -52,7 +55,11 @@ Note that mostly raid 1 devices consisting of 2 drives should be converted to
### Raid 5 ### Raid 5
Raid 5 creates a raid device with distributed parity. Raid 5 creates a raid device with distributed parity and is set to have at least
For `n>1` drives with the same size it creates a raid device with the size `n-1` 3 drives.
drives. The space efficiency is `1-(1/n)` and the fault tolerance is `1` drive failure.
For `n=2` raid 5 and [raid 1](#raid-1) are basically the same. The read perfromance is `n` and the write performance `1/4` for single sector
and `n-1` for full stripe.
In the special case of 2 drives in a raid 5 it is functionally the same as
[raid 1](#raid-1).