Extending RAID

Prepare new disk                 Need to partition? Do it now. I'll wait... 
 Setup: The current RAID has 4 drives and we want to add a 5th drive. The current array is "md111" and we have already checked drives on the system lsblk to see which drive we will be adding "sdd1" 
 Add disk to RAID mdadm --add /dev/md111 /dev/sdd1 
 mdadm --add /current/drive/array (array that already has the other raid dirves in it) /new/drive/to/add (the 1 drive that you will be adding) 
 Grow RAID: mdadm --grow --raid-devices=4 /dev/md111 This will grow your current array to accept a new drive 
 Now that you have expanded the underlying partition, you must now resize your filesystem to take advantage of it. You may want to perform an fsck on the file system first to make sure there are no underlying issues before attempting to resize the file system 
 Integrity Check:  e2fsck -f /dev/md111 
 Resize array:  resize2fs /dev/md111 
 Mount it:  mount /dev/md111 /your/new/local/location 
 Check RAID rebuild status or Current status cat /proc/mdstat 
 Sources you can use: https://raid.wiki.kernel.org/index.php/Growing