When booting from an alternate root pool disk, ensure that all the root pool's disks are attached and online so you can boot from any of the disks, if necessary. On most systems, you cannot boot directly from a disk that has been detached, or boot from an active root pool disk that is currently offline.
The primary disk in a mirrored root pool is typically the default boot device. To boot from a different device, you must specify that disk when issuing the command to boot.
If you want to change the default boot device, first display the pool's configuration to select the device you want. Then, at the OK prompt, update the system's PROM with the selected device. Boot the system and confirm that your selected device is the active boot device.
The following example assigns c1t1d0 as the default boot device.
$ zpool status pool: rpool state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM rpool ONLINE 0 0 0 mirror-0 ONLINE 0 0 0 c1t0d0 ONLINE 0 0 0 c1t1d0 ONLINE 0 0 0 ... ok boot /pci@7c0/pci@0/pci@1/pci@0,2/LSILogic,sas@2/disk@1
After the system is rebooted, you would confirm which active boot device is in the system.
$ prtconf -vp | grep bootpath bootpath: '/pci@7c0/pci@0/pci@1/pci@0,2/LSILogic,sas@2/disk@1,0:a'
On x86 based systems with a modern BIOS where the boot disk order is properly set, the system boots automatically from the second device if the primary root pool disk is detached, offline, or unavailable. In such systems, you merely need to confirm which active boot device is in the system, as shown in the following example.
$ prtconf -v|sed -n '/bootpath/,/value/p' name='bootpath' type=string items=1 value='/pci@0,0/pci8086,25f8@4/pci108e,286@0/disk@0,0:a'