CentOS7 boot from USB thumbdrive.
Ref. to How to install using USB Using Windows Starting with CentOS 6.5, one can create a bootable USB key simply by installing the ISO file on the key using a program such as Win32 Disk Imager . This will delete all information already on the key. Downoad: Win32 Disk Imager Install Win32 Disk Imager Transfer the ISO image to USB using above Win32 Disk Imager. Click on "Write" button. Ready to boot and install from your USB key.