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');
...

Defining DISK_BOOT_DEV is important because it might be used in some filesystem layouts to define the name of the root partition. An example illustrating this can be found in site/filesystems/classic_single_root :

variable DISK_BOOT_PARTS = list('root');
variable DISK_VOLUME_PARAMS = {
      t = dict();
      t['root'] = dict('size', -1,
                       'mountpoint', '/',
                       'type', 'partition',
                       'device', DISK_BOOT_DEV+to_string(index('root',DISK_BOOT_PARTS)+1));
      t;
};

In this example, if DISK_BOOT_DEV is 'sda', then the name of the device of the root partition will be 'sda1'.