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I'm reading up on setting up a RAID with two drives on my Debian install, and that the /proc/mdstat file contains a list of the supported raid types by the kernel next to 'Personalities'. Running cat /proc/mdstat however shows only blank space where the supported RAID types should be. I'm running Debian Testing. Does my kernel really not support any RAID types or am I missing something here? Thanks.

Here's the full output of the cat, just in case someone needs it:

cat /proc/mdstat

Personalities : 
unused devices: <none>

My kernel version is 4.16.0-2-amd64

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I have a RAID array set up on a Raspberry PI (don't ask why), but when I run

cat /proc/mdstat

it prints

Personalities : [raid0] 
md0 : active raid0 my_raid_devices
      num_of blocks super 1.2 512k chunks

The my_raid_devices and num_of refer to the RAID devices I'm using and number of blocks available respectively; but when I read the same file on another system it reads

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
unused devices: 

This system has no RAID arrays set up, but notice the Personalities differences. I believe this has to do with kernel differences as well; the Pi is running kernel 4.14.34, while the other system is running 4.9.0-3. They are both running Debian (Raspbian for the Pi, of course).

Post your kernel release, by doing

uname -r
It doesn't matter if you are administrator or not.

EDIT: Can you attempt to build a array even with this issue? If not, maybe try downgrading to a different kernel?

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  • I've edited my version into the question Jul 18 '18 at 20:19
  • Also I'm actually very curious as to why you have RAID configured on a Pi. Jul 18 '18 at 20:20
  • Extra storage, because I happened to have a bunch of flash drives lying around and I needed a small network-accessible storage system Jul 18 '18 at 20:25
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The kernel modules providing the MD raid services are only loaded when needed. /proc/mdstat reflects what is available at the current point in time.

You can force the loading of the raid modules:

sudo modprobe raid0
sudo modprobe raid1
sudo modprobe raid456
sudo modprobe raid10
sudo modprobe linear

After doing that /proc/mdstat will show all these raid methods.

In normal use the kernel automatically loads the necessary modules, so you won't need to manually modprobe these.

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