When NValias need is:

In case system can not boot from primary disk and it is needed to make another boot disk to access the data , nvalias command is used.

nvalias command makes the device alias and assigns an alternate name to a physical disk. Physical address of target disk is required which can be had by show-disk command on ok>.

ok> nvalias disk7 /iommu@f,e0000000/sbus@f,e0001000/dma@3,81000/esp@3,80000/sd2,0

The new aliased disk can be named as boot disk or can be used for booting by referring its name

ok> setenv boot-device disk7

ok>reset

or

ok> boot disk7