On 30/11/2020 20:05, David T-G wrote:

You don't see any "filesystem" or, more correctly, partition in your

   fdisk -l

output because you have apparently created your filesystem on the entire
device (hey, I didn't know one could do that!). 

That, actually, is the norm. It is NOT normal to partition a raid array.

It's also not usual (which the OP has done) to create a raid array on 
top of raw devices rather than partitions - although this is down to the 
fact that various *other* utilities seem to assume that an unpartitioned 
device is free space that can be trampled on. Every now and then people 
seem to lose their arrays because an MBR or GPT has mysteriously 
appeared on the disk.

That conclusion is
supported by your mount point (/dev/md127 rather than /dev/md127p1 or
similar) and your fstab entry (same).

So the display isn't interesting, although the logic behind that approach
certainly is to me.

Your approach seems to be at odds with *normal* practice, although there 
is nothing wrong with it. At the end of the day, as far as linux is 
concerned, one block device is much the same as any other.

Cheers,
Wol