$ sudo mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/nvme0n1p1 --write-mostly /dev/sdc1
mdadm: Note: this array has metadata at the start and
    may not be suitable as a boot device.  If you plan to
    store '/boot' on this device please ensure that
    your boot-loader understands md/v1.x metadata, or use
    --metadata=0.90
mdadm: /dev/sdc1 appears to be part of a raid array:
       level=raid1 devices=2 ctime=Sat Jan  9 15:22:29 2021
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
@KE:

@KT:Listing 9: View the RAID Volume
@LI:§§nonumber
$ sudo mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Sat Jan  9 15:52:00 2021
        Raid Level : raid1
        Array Size : 244065408 (232.76 GiB 249.92 GB)
     Used Dev Size : 244065408 (232.76 GiB 249.92 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent
     Intent Bitmap : Internal
       Update Time : Sat Jan  9 15:52:21 2021
             State : clean, resyncing
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0
Consistency Policy : bitmap
     Resync Status : 1% complete
              Name : dev-machine:0  (local to host dev-machine)
              UUID : 833033c5:cd9b78de:992202ee:cb1bf77f
            Events : 4
    Number   Major   Minor   RaidDevice State
       0     259        2        0      active sync   /dev/nvme0n1p1
       1       8       33        1      active sync writemostly   /dev/sdc1