Using the following SQL you can monitor the progress of RMAN process, as channels completes creating the backpiece new sessions are created so overall progress can be monitored by looking at where context = 3 as in the case below it shows the overall progress is 38.05% complete.

— works in 8i/9i/10g.

SQL> SELECT sid, serial#, context, sofar, totalwork,
round(sofar/totalwork*100,2) “% Complete”
FROM v$session_longops
WHERE totalwork 0
and upper(opname) like ‘%RMAN%’
and sofar totalwork;