I need to remove SDI and SDO from the array using the command line because OMV is not working properly. How could I do ?
Also, how could I later add the same drives to the RAID6 array MD127 via command line ?
What I do is first I fail the drive in the array and then I remove it and then I shred it and then I assemble using the new one. You may need to change the SDC and MD, int he example below I remove C and add Q to md127 with a and b already in it.
mdadm --fail /dev/md127 /dev/sdc
mdadm --remove /dev/md127 /dev/sdc
shred -v -n 1 /dev/sdc
mdadm --assemble /dev/md127 /dev/sd[abq] --verbose --force
If you need to unmount and stop the array:
mdadm --stop /dev/md127
Good luck, please be aware that you can lose all of your raid if not done properly.