Booting From a ZFS Root File System

Both SPARC based and x86 based systems boot with a boot archive, which is a file system image that contains the files required for booting. The root file system that is selected for booting contains the path names of both the boot archive and the kernel file.

In the case of a ZFS boot, a device specifier identifies a storage pool, not a single root file system. A storage pool can contain multiple bootable ZFS root file systems. Thus, you must specify a boot device and a root file system within the pool that was identified by the boot device.

By default, a ZFS boot process uses the file system that is defined in the pool's bootfs property. However, you can override the default file system. On SPARC systems, you can use the boot -Z command and specify an alternate bootable file system. On x86 systems, you can select an alternate boot device from the BIOS.

If you replace a root pool disk with the zpool replace command, you must install the boot information on the replacement disk. However, installing the boot information is not required if you merely attach additional disks to the root pool.

To install the boot information, use the bootadm command in one of the following ways:

• To install the boot information on the existing root pool's disk, use the following command:

  $ bootadm install-bootloader

• To install the boot information on an alternate pool, use the following command:

  $ bootadm install-bootloader -P alt-root-pool