11.2u5 can't boot with error 6

[szdefine]

i have a freenas sever for half a year always works fine .but yesterday i reboot the sever, just can't boot in the system(see the blew pic) .

i am a newbie of freenas ,how can i do next? thanks

 

[szdefine]

it seems like the da12 failed ,can i just replace it in this situation?

 

[szdefine]

it solved ! da12 is the boot usb stick ,reinstall freebsd img and restore config works fine.