Prepare discs for new array with parted.

root@host:~# parted -a optimal /dev/sde
GNU Parted 2.3
Using /dev/sde
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) mklabel gpt                                                      
Warning: The existing disk label on /dev/sde will be destroyed and all data on this disk will be lost. Do you want to continue?
Yes/No? Yes                                                               
(parted) mkpart primary 1 -1                                  
(parted) align-check 
alignment type(min/opt)  [optimal]/minimal? opt        
Partition number? 1                       
1 aligned
(parted) q            
Information: You may need to update /etc/fstab.      

Create RAID10 when disks are ready:

root@cyfrowygabinet:~# mdadm -v --create /dev/md0 --level=raid10 --raid-devices=4 /dev/sdb1 /dev/sdc1 /dev/sde1 /dev/sdd1 
mdadm: layout defaults to n2
mdadm: layout defaults to n2
mdadm: chunk size defaults to 512K
mdadm: size set to 2930133504K
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.