|
|
|
@ -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).
|
|
|
|
|
