HardDisksManagement
Specifying the disk that will used to boot the machine
The path is :
/hardware/harddisks/<harddisk_name>/boot
It is a boolean that is used to define the value of DISK_BOOT_DEV. Have a look at the code of the template site/filesystems/layout :
...
variable DISK_BOOT_DEV ?= boot_disk();
variable DISK_BOOT_DEV ?= {
if (exists('/hardware/harddisks/sda')) {
return('sda');
...