I am not entirely sure RHEL reaction would be but in a normal set up the /boot is simply a directory and not a boot sector which can be moved and revised in /etc/fstab and /boot/grub/grub.conf. The Grub in the MBR is hard coded to hard disk address of your current sdb1 so you will need to do a "set up" with Grub again in a Grub shell or run "grub-install" in a RHEL root terminal.
It should be relative safe to have both tested and then do a switch over when you are satisfied with the result.
I outline the key steps below. Please check your /boot/grub/device.map to make sure the device name in Linux and Grub. Below I have assumed (hd0) is /dev/sda.
(1) Say you managed to resize disk sda and get some hard disk space to create a sda2, format it in Ext2/3/4, mount it and copy the content of /boot across, including all subdirectories to mounted sda2.
(2) Edit /boot/grub/grub.conf and change the partition reference in the "root" statement. That reference should in Grub and for the 1st partition of the second disk it should be (hd1,0). The equivalent for sda2 should be (hd0,1) as Grub1 counts from 0. The /boot/grub/device.map should confirm (hd0) is /dev/sda and (hd1) =/dev/sdb. If not adjust to suit.
(3) Edit /etc/fstab and replace the partition reference for /boot with device /dev/sda2. RHEL is likely to use label or uuid reference for device name of /boot. It is quite acceptable to use the traditional Linux device name /dev/sda2 as I do this all the time.
(4) Invoke a Grub shell in a RHEL root terminal and issue the following Grub commands
Code:
root (hd0,1)
setup (hd0)
quit
I assume /dev/sda is (hd0) so please check sda is your first boot disk.
(4a) Instead of using a Grub shell the set up can be achieved in a root terminal by command
Code:
grub-install /dev/sda
The system should point to sda2 on a reboot. Your sdb1 would only be visible if you mount it.
If thing works satisfactory you can proceed to use sdb1 for other purpose.
If RHEL objects to the change you may need to amend Selinux. If that is not possible you can always revert back to sdb1.
I have moved RHEL and Fedora entirely to another partitions at the cost disabling Selinux temporarily.
In a nutshell you don't move the boot sector. You simply re-hard coded Grub in the MBR to the hard disk address of a new /boot partition.