I have received a Veritas Appliance which I wanted to install Flex OS on it.
I used this link from Veritas to create a bootable disk and received the Flex ISO software from my colleague.
To boot from USB, you just need to select DEL key once the Bios post message asks you to invoke a key if needed.
The installation is a straight forward process and automated by script until the OS is installed successfully on the appliance.

The issue I faced was that , once the appliance would boot from USB, during the installation was getting stuck at:
“Started cancel waiting for multipath siblings of sdx”

I tried multiple option to sort out this issue which seems many people faced this issue in RHCE (FLEX based OS) but they were of no use.
Finally, I was able to sort out the issue, logging into remote management (you need to configure the BMC in bios first) opened the screen session to appliance GUI and attached the ISO to Media storage (virtual media storage.
This time the installation continued and finished successfully.

Ahmad,