Backing up data is main source of income after line's cut (9)
I believe the answer is:
archiving
'backing up data is main source of income' is the definition.
I can't tell whether this definition defines the answer.
'line's cut' is the wordplay.
'line' becomes 'arc' (arc is a kind of line).
'cut' becomes 'hiving' (I can't justify this - if you can you should give a lot more credence to this answer).
'arc'+'hiving'='ARCHIVING'
'after' is the link.
Can you help me to learn more?
(Another definition for archiving that I've seen is " Keeping a record".)