Question about a mismatch between documentation and how mdadm currently works.

[Tom H]

On Sat, Apr 1, 2017 at 9:50 PM, Kevin O'Gorman <kogorman at gmail.com> wrote:
>
> I'm fooling around with RAID on Linux for the first time. Lots to
> learn. I have one issue that keeps coming up with creating RAID arrays
> with mdadm.
>
> The documentation I have all says to create arrays with something like
> mdadm --create /dev/md0 (and some more stuff) and what follows really
> does indicate they expect the array to appear as /dev/md0. What
> happens when I try it is that the array is created as /dev/md127. If I
> create two arrays, the next one is /dev/md126.
>
> Likewise, if I assemble a RAID array, they go to the high numbers no
> matter what my command-line says.
>
> What's up with this? Is it historical? Is something just ignoring that
> part of the command line? Is that part even required?

# mdadm --create /dev/md0 -l 1 -n 2 /dev/sdb /dev/sdc
# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
[raid4] [raid10]
md0 : active raid1 sdc[1] sdb[0]
 1047552 blocks super 1.2 [2/2] [UU]
#

A random shot in the dark: is your hostname set properly?

Or, more usefully, does running "examine" output your actual hostname.
So for my array above, mdadm -E /dev/sd{b,c}