Boot from USB drive to load RHEL on a SSD

[kenyloveg]

Hi, there

 I'm strugling to boot RHEL on a SSD with my HPE MicroServer Gen8.

Here is some related information.:

 Installed RHEL8.1 on a 128GB SSD(SATA5 /dev/sdd), a 4GB USB drive on USB port(/dev/sdb), and 2x5TB HDD (SATA 1&2, /dev/sda /dev/sdc)

I set bios to boot USB drive first, so it can chainload to boot SSD (RHEL 8.1). I've tried this method:

http://jarrodla.blogspot.com/2014/04/hp-microserver-gen8-boot-from-5th-sata.html

But the file system seems different, also grub2 commands are not fitting the current RHEL 8.1.

Would somebody help me on this?

Thanks and have a good day.