Add to the syslinux.cfg’s append line live-media=/dev/sdb1 if you have one hard drive

live-media=/dev/sdc1 if you have two hard drives

live-media=/dev/sdd1 if you have three hard drives

An example:

menu label Puolanka Remaster sdc1
kernel /casper/vmlinuz
append initrd=/casper/initrd.gz boot=casper locale=fi_FI.UTF-8 live-media=/dev/sdc1