1) Boot a server in rescue mode
2) Check partitions

[root@rescue /]# fdisk -l

Disk /dev/sda: 3.7 TiB, 4000787030016 bytes, 7814037168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 961524F0-9337-4FC8-B4AD-C65D8750BF58
Device          Start        End    Sectors  Size Type
/dev/sda1        2048    1048575    1046528  511M EFI System
/dev/sda2     1048576 7812980735 7811932160  3.7T Linux RAID
/dev/sda3  7812980736 7814027263    1046528  511M Linux swap
Disk /dev/sdb: 3.7 TiB, 4000787030016 bytes, 7814037168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 129DD84C-61D3-464B-910D-E87055EE5C4A
Device          Start        End    Sectors  Size Type
/dev/sdb1        2048    1048575    1046528  511M EFI System
/dev/sdb2     1048576 7812980735 7811932160  3.7T Linux RAID
/dev/sdb3  7812980736 7814027263    1046528  511M Linux swap
Disk /dev/md2: 3.7 TiB, 3999709200384 bytes, 7811932032 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes



3) mount partitions


root@rescue:~# mount /dev/md2 /mnt/
root@rescue:~# mount --bind /dev/ /mnt/dev
root@rescue:~# mount --bind /sys /mnt/sys
root@rescue:~# mount --bind /proc /mnt/proc
root@rescue:~# chroot /mnt
[root@rescue /]# mount /dev/sda1 /mnt/boot/efi/


4) grub2 intallation


[root@rescue /]# grub2-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=grub --recheck
Installing for x86_64-efi platform.
Installation finished. No error reported.


5) grub.cfg configuring


[root@rescue /]# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/bzImage-3.14.32-xxxx-grs-ipv6-64
Found linux image: /boot/vmlinuz-3.10.0-693.5.2.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-693.5.2.el7.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-693.2.2.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-693.2.2.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-1e98a4cc1263468b9f9a12e365316b95
Found initrd image: /boot/initramfs-0-rescue-1e98a4cc1263468b9f9a12e365316b95.img
Done


6) exit and reboot

ctrl+C
ctrl+D
root@rescue:~# reboot