Have been having this argument for a while. Is saying "really redundant" or "very redundant" or something along those lines redundant in and of itself?
No because some things are more redundant than others. Safety critical applications are often very redundant:
In many safety-critical systems, such as fly-by-wire and hydraulic systems in aircraft, some parts of the control system may be triplicated, which is formally termed triple modular redundancy (TMR).
Likewise a sentence with three words where one would do would also be very redundant.
A very redundant work might also just have multiple redundancies.
If you regard 'redundant' as an absolute adjective, like 'dead' or 'pregnant' or 'unique', then logically you should not precede it with a modifier such as 'very', because that word would be superfluous, and thus redundant. If you think that there may be degrees of redundancy, then perhaps some examples might be of higher degree than others.
“Very redundant” simply relates to extent, as Laurel and others have noted.
“Really redundant” is more interesting. At the risk of redundancy, let me offer the following perspective.
The simple definition doesn’t (really) do it justice:
really adjective 1 In actual fact, as opposed to what is said or imagined to be true or possible. ‘so what really happened?’ 2 (as submodifier) Very; thoroughly. ‘a really cold day’ - ODO
In practice, where a word can be used in multiple senses, ‘really’ can (but doesn’t always) switch the meaning to the less-common sense when the rest of the sentence is repeated.
In a wax museum, suppose a guide wanted to introduce a statue of the city’s most upstanding member, John:
- “John is a model citizen” says something complimentary about John; but if it is followed by
- “John is really a model citizen”, it could be for emphasis, or it could be pointing out that this is just a model of John, not the person in the flesh.
In some cases, such as that of your example, the first instance isn’t even needed. The non-technical parsing of redundant system suggests wastage - e.g. “The second insurance policy was redundant. The insurer won’t pay twice what you lost.” However, the technical parsing de-emphasises wastage and simply communicated that the system has multiple ways of achieving a given objective - e.g. carrying two pens in case one runs dry. Far from being considered undesirable, aircraft control and other safety-critical systems are routinely engineered to purposely and purposefully include redundancy.
Nevertheless, in a technical presentation, “the fifth box is really redundant” sidesteps the technical parsing and favours the non-technical parsing, suggesting ‘wastage’.
So to answer your question, “really redundant” isn’t “redundant”. It is either more emphatic or, alternatively, it induces a different parsing.
The words really and real are always redundant, so far as semantics is concerned. Something is really X (or a real X) if and only if it is X. It is, strictly speaking, impossible to be X without really being X.
The words really and real, however, do have an important role to play, so far as pragmatics is concerned. Whenever the context is such that one's audience may have doubts as to whether something is X, saying that it is really X has a purpose: it conveys that the speaker has considered these doubts and can reassure the audience that the thing is X, and not merely something that falsely appears to be an X.
To apply this general answer to the OP's specific case: the word really in the phrase really redundant is, indeed, semantically redundant, but it can still, in the right kind of context, perform a worthwhile role of letting the audience know that the speaker is aware that there may be doubts as to whether the thing is redundant, and can reassure them that, notwithstanding these doubts, it is redundant.
The phrase very redundant raises entirely different questions, which have already been adequately addressed in Michael Harvey's and Laurel's answers on this page.