It depends on the version of Tru64 you are using.
For Tru64 v4.0 if you can work out what the special device file name should be, then:
cd /dev
./MAKEDEV rz<x><n> (where x is a letter, n is a number
For Tru64 v5.0 & v5.1 the special device files often get created automatically. But check out the man pages for dsfmgr , hwmgr , scsimgr.
I hope that helps
Mike