Your TrueNAS pool keeps growing, and you suspect the same files are sitting in several datasets. Many people assume ZFS deduplication already takes care of that. It doesn't, at least not the way you'd expect, and counting on it leaves you with either wasted RAM or a NAS still full of copies.
Block dedup is a storage feature, not a cleanup tool
ZFS deduplication works at the block level. It avoids writing the same block twice on the pool, invisibly, to save disk space. It comes at a real cost: it's RAM-hungry (commonly cited around 1 to 5 GB of RAM per TB of data), it maintains a deduplication table that grows as your data grows, and TrueNAS's own guidance frequently warns against turning it on unless you really know your dataset will benefit. It also runs inline, on newly written data only, so it does nothing about the duplicates already sitting on your pool. None of this produces a human-readable answer to the question you actually have: which of my files are duplicates, and how much space would I get back by removing them?
File dedup is what you're really after
What most people want is file-level deduplication: spotting that the same photo, video or document is sitting in three different folders, and being able to look at the list and clean it up. That has nothing to do with the ZFS block layer. It's a read-only scan of your files followed by a deliberate cleanup, and it doesn't require touching your pool, your RAM budget or your dataset settings.
How NAS Ranger handles it, without touching ZFS
NAS Ranger connects to your TrueNAS shares over SMB and identifies duplicates by content fingerprint, so identical files are found regardless of name, date or folder. It never alters your pool, datasets or ZFS options. You see every duplicate group and the exact space you'd reclaim. For the detail of content matching, see how to find duplicate files.
A deliberate, reversible cleanup
You act on many files at once, and nothing is destroyed in place. Confirmed duplicates are moved to a trash folder on the share, a rename, so you review before purging. Here's why that stays safe. And since the app runs on your computer over SMB, there's nothing to install on TrueNAS and a system update can't take it away.
Try it free: scan your TrueNAS shares, see every duplicate and the gigabytes you can reclaim, before touching a single file.