How to Record the Path to the Alternate Boot Device

When you are mirroring root (/), you might need the path to the alternate boot device later if the primary device fails. The process for finding and recording the alternate boot device differs, depending on your system's architecture. See SPARC: Example—Recording the Alternate Boot Device Path or x86: Example—Recording the Alternate Boot Device Path.

SPARC: Example—Recording the Alternate Boot Device Path

In this example, you determine the path to the alternate root device by using the ls -l command on the slice that is being attached as the second submirror to the root (/) mirror.

# ls -l /dev/dsk/c1t3d0s0
lrwxrwxrwx 1  root root  55 Mar 5 12:54  /dev/rdsk/c1t3d0s0 -> \ 
../../devices/sbus@1,f8000000/esp@1,200000/sd@3,0:a

Record the string that follows the /devices directory: /sbus@1,f8000000/esp@1,200000/sd@3,0:a.

Edit the string to change the major name (sd, in this case) to disk, resulting in /sbus@1,f8000000/esp@1,200000/disk@3,0:a. If the system uses an IDE bus, the original full path might look like

$ ls -l /dev/dsk/c0t0d0s0 
lrwxrwxrwx 1 root root 38 Mar 13 15:03 /dev/dsk/c0t0d0s0 -> \
../../devices/pci@1f,0/ide@d/dad@0,0:a

After changing the major name dad to disk, you would have /pci@1f,0/ide@d/disk@0,0:a

You can use the OpenBoot^TM Prom nvalias command to define a “backup root” device alias for the secondary root (/) mirror. For example:

ok  nvalias backup_root /sbus@1,f8000000/esp@1,200000/disk@3,0:a

Then, redefine the boot-device alias to reference both the primary and secondary submirrors, in the order in which you want them to be used, and store the configuration.

ok printenv boot-device
boot-device =         disk net
ok setenv boot-device disk backup-root net
boot-device =         disk backup-root net
ok nvstore

In the event of primary root disk failure, the system would automatically boot to the second submirror. Or, if you boot manually, rather than using auto boot, you would only enter:

ok  boot backup_root

x86: Example—Recording the Alternate Boot Device Path

In this example, you would determine the path to the alternate boot device by using the ls -l command on the slice that is being attached as the second submirror to the root (/) mirror.

# ls -l /dev/dsk/c1t0d0s0
lrwxrwxrwx 1  root root  55 Mar 5 12:54  /dev/rdsk/c1t0d0s0 -> ../.
./devices/eisa/eha@1000,0/cmdk@1,0:a

Here, you would record the string that follows the /devices directory: /eisa/eha@1000,0/cmdk@1,0:a