reduces the settle time for a usb device from 5 seconds to 1 second. This is a workaround to get the USB devices ready in time for the raid detection.rootflags=data=writeback
forces the kernel to mount the drive in data writeback mode. Without this option booting will fail when it tries to remount the partition read-write.rootdelay=5
delay root to allow the usb drivers to pop on
Howto: Boot Linux with a USB Flash Drive Raid as the RootFS
How can I boot from a USB hard drive without BIOS support and no HDD?