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Description of problem:
After installing on a USB drive (in expert mode), RHEL does not boot. The problem is caused by the lack of the USB drivers in the initial ramdisk image (inird).
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Install RHEL in expert mode to a USB drive
Actual Results: Panic, since root was not mounted
Expected Results: Normal boot
The problem is well known, solution is to add the USB drivers to the inital ramdisk image: http://www.simonf.com/usb/ . Workaround is very time-consuming.
Installs to USB disks are not supported, this is why they're not allowed by default.