When I run “grub2-mkconfig” on my CentOS-7.1 desktop I get the warning (4 times)
/usr/sbin/grub2-probe: error:
cannot find a GRUB drive for /dev/block/8.
Check your device.map.

What exactly does this mean?

My device map looks perfectly normal to me:
[root@helen ~]# cat /boot/grub2/device.map
(hd0) /dev/sda
(hd1) /dev/sdb

This makes me reluctant to boot into CentOS-7.2.

An additional, possibly related, query. When I run grub2-mkconfig it lists various OS’s it finds:
========================Found Windows 7 (loader) on /dev/sda1
Found CentOS Linux release 7.1.1503 (Core) on /dev/sda12
Found Windows 7 (loader) on /dev/sdb1
Found CentOS release 6.5 (Final) on /dev/sdb5
Found CentOS release 5.6 (Final) on /dev/sdc7
done
========================Why does it not list CentOS 7.2 since it
========================Found linux image: /boot/vmlinuz-3.10.0-327.4.4.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-327.4.4.el7.x86_64.img
========================