If it’s just buckets of data, mergerfs can pool the drives together, and then you can dedupe the whole lot.
Or consider buying a surplus 20tb drive, copy everything to it, dedupe the 20, write back to the 4+4+2 as cold spares. Those surplus drives are $10-14 per tb and I’ve had fantastic luck with them.
If it’s just buckets of data, mergerfs can pool the drives together, and then you can dedupe the whole lot.
Or consider buying a surplus 20tb drive, copy everything to it, dedupe the 20, write back to the 4+4+2 as cold spares. Those surplus drives are $10-14 per tb and I’ve had fantastic luck with them.