How to Find Duplicate Files on a Synology or QNAP NAS

TL;DR: On a Synology, turn on Find duplicate files in a Storage Analyzer report profile and read the Duplicates tab of the report. It lists up to 5,000 candidates and removes nothing. QNAP's documentation shows no duplicate finder; QNAP's own blog points to a command-line tool. Storage deduplication (ZFS, QuTS hero) saves space underneath but never tells you which files are copies. Whatever finds them, confirm by content and send extras to the share's recycle bin, not to permanent deletion.

Duplicates pile up on a shared NAS. Someone copies a client folder "just in case" before a reorganization. A laptop backup lands on the same share as the files it backed up. Nobody notices until the volume is nearly full.

Disclosure: The Drive AI publishes this guide and makes the NAS helper described near the end. Everything before it uses tools your NAS already has or free ones. Vendor features are described from Synology's, QNAP's and TrueNAS's own pages as of October 2026.

How do you find duplicate files on a NAS?

Use the NAS's own report first if it has one: Synology's Storage Analyzer lists duplicate candidates per report. QNAP documents no equivalent, so you need a tool that compares file contents, run on the NAS or from a computer. Treat every list as candidates until the contents match, and remove copies into the recycle bin.

Does Synology have a duplicate file finder?

Yes, inside Storage Analyzer. A report profile can include a duplicate files check, and the finished report has a Duplicates tab, which Synology describes as listing "duplicated files found in the system for the convenience of organizing or deleting unnecessary copies." (Synology Knowledge Center) The report itself doesn't remove anything. You decide what goes.

Step 1: Create a report profile

In DSM 7, open Storage Analyzer > Report Profile and click Create. Give the task a name and an email address for the report. Under shared folders, choose Only analyze specific shared folders if you want to start with one share; scanning everything takes longer. (Synology Knowledge Center)

Step 2: Turn on the duplicate check

Tick Find duplicate files when generating reports and set the maximum number of duplicates to list. Synology says a larger number takes longer to process. You can also choose to ignore file name or modified time to speed up the analysis. Ignoring the file name catches copies saved under different names, the ones you can't find by hand.

Step 3: Read the Duplicates tab

Run the task, open the report, and go to File > Duplicates. The same File section has Least Recently Accessed Files, up to 200 of them, which is the quickest look at the cold data on the volume. Synology notes its accuracy depends on the volume's access-time setting.

The limits. Synology's specifications cap each report at 5,000 duplicate files, and Hybrid Share folders aren't included in usage reports. (Synology) Synology's help doesn't say whether the comparison reads file contents or only compares attributes such as size, name and modified time, so treat each group as a candidate and confirm it before anything is removed. Synology also notes that file system level deduplication might affect the results of usage reports.

Does QNAP have a duplicate file finder?

Not one we could find in QNAP's documentation as of October 2026. QTS and QuTS hero have three features with "duplicate" or "dedup" in the name, and none of them lists duplicate files:

• File Station's Duplicate File Name Policy decides what happens when you upload, copy or move a file into a folder that already has one with the same name: ask, rename, skip or overwrite. (QNAP documentation) It prevents name clashes. It doesn't find copies that already exist.
• QuDedup is part of Hybrid Backup Sync 3. It deduplicates backup data, not the files on your shares. (QNAP)
• QuTS hero deduplication works on data blocks inside a shared folder or LUN and needs at least 8 GB of memory. QNAP's example of two identical files ends with only their matching blocks being deduplicated: both files are still there. (QNAP FAQ)

QNAP's own answer is on its blog. A March 2026 post, updated in August 2026, walks through installing jdupes, a command-line duplicate finder, over SSH, and says plainly that "jdupes is not an official QNAP utility." (QNAP Blog) The catch is how it deletes. QNAP's Network Recycle Bin catches deletions made through Samba, AFP, FTP and File Station, so a delete run from the command line doesn't land in @Recycle. (QNAP documentation) Run jdupes to list duplicates first, and remove the copies through File Station or a mapped drive.

What about TrueNAS and Unraid?

Neither documents a built-in duplicate file report. TrueNAS offers ZFS deduplication, which stores "just one copy" of data blocks that several files share; it's a storage setting, not a list of files. TrueNAS warns that "when data is not sufficiently duplicated, deduplication wastes resources" and that the dedup table must fit in RAM. (TrueNAS documentation) On Unraid, the Community Apps catalogue has third-party tools, such as Unraid-Duplicate-File-Handler, which looks for the same file on more than one array disk or pool. (Unraid Community Apps)

Is storage deduplication the same as finding duplicate files?

No. Storage deduplication is invisible: the file system notices identical blocks and stores them once. Every copy stays in every folder, people still open the wrong one, and the clutter is untouched. Finding duplicate files is visible: you get a list of identical files, choose which copy to keep, and remove the rest.

Dedup can save space at a hardware cost. A NAS people can find things on needs the list.

How do you tell if two files on a NAS are really identical?

Compare a content hash, not the name. A hash such as SHA-256 is a fingerprint calculated from every byte of a file. Two files with the same SHA-256 are identical, whatever they're called and wherever they sit.

Name, size and date are good for a candidate list and bad for proof: two different scans can share a size, and the same contract saved twice gets two modified dates. The longer explanation, including near-identical files that aren't duplicates, is in our guide to duplicate file detection.

How do you choose which copy to keep and remove the rest safely?

Decide the rule before you start, take a snapshot, and remove into the recycle bin.

Pick the copy that wins. The oldest is usually the original. The one in the folder that matches your structure is usually the one people expect to find. Avoid keeping the copy in Old server or a personal folder, even if it's newest. The same rules apply as when you find duplicate files in Google Drive.

Check that the recycle bin is on. On Synology it's set per shared folder under Control Panel > Shared Folder > Edit > Enable Recycle Bin, and you restore from the share's #recycle folder in File Station. (Synology Knowledge Center) On QNAP, deleted files go to the share's @Recycle folder and you restore them from Recycle Bin in File Station, as long as the recycle bin is enabled for that share. (QNAP documentation)

Snapshot first. A snapshot of the share before the cleanup turns any mistake into a restore. It's step one of our checklist to clean up a shared office NAS, which also covers moving duplicates to a review folder before anything is deleted.

Ask before removing a copy someone uses. A signed contract can sit in both a client folder and a Signed 2025 folder on purpose. Mapped drives, shortcuts and linked spreadsheets point at paths, so a removed copy can break something quietly.

How does The Drive AI find duplicates on a NAS?

The Drive AI runs a small helper on the NAS as a Docker container, so the work happens where the files are. Here's how it goes.

Step 1: Pair the NAS

In The Drive AI, go to Settings > Agent > Pair a device. It gives you a Docker compose file with the pairing code filled in. Start it in Container Manager on a Synology, Container Station on a QNAP, or Docker on TrueNAS or Unraid, and mount the shares you want. The helper connects out, so no port is opened. Setup is covered in how to organize a Synology NAS with AI.

Step 2: Ask in a sentence

Find duplicate files on the Clients share. Keep the oldest copy of each and move the rest to _Duplicates to review.

The helper computes a SHA-256 hash of each file on the NAS itself. Only the fingerprints leave the NAS; files aren't uploaded to find duplicates. Files the helper hasn't hashed yet are hashed in the background when you ask.

The answer groups identical files, largest reclaimable space first, with a summary: how many groups, how many redundant copies, how much space they take, and how many files have no fingerprint yet. Look-alikes, such as a re-exported PDF a few bytes larger than the original, are listed separately to compare. They're never removed as duplicates, because their bytes differ. You can also ask for the groups as a spreadsheet and review it first.

Step 3: Approve the plan

You choose the keep rule: oldest, newest, the copy in the shallowest folder, or alphabetical. The extra copies go to the share's own recycle bin (#recycle on Synology, @Recycle on QNAP) or into a folder you name. The whole cleanup is shown as one plan, and nothing changes until you approve it. Undo puts moved files back; files sent to the recycle bin are restored from File Station like any other deletion. If the share has no recycle bin, the helper moves files instead of deleting them.

The limits. Duplicates are matched within one source: a file on the NAS isn't matched against its copy in Dropbox or OneDrive, because each platform fingerprints files differently. A file that hasn't been hashed yet isn't covered until it is. And connecting a NAS needs the Max plan or a Team plan. The NAS integration page has the short version.

Frequently Asked Questions

Does Synology Storage Analyzer delete duplicate files?

No. Storage Analyzer generates reports. With Find duplicate files ticked in a report profile, the report's Duplicates tab lists up to 5,000 duplicate files. You review the groups and remove copies yourself, for example in File Station, where deletions go to the shared folder's recycle bin if it's enabled.

How do I find duplicate files on a QNAP NAS?

QNAP's documentation shows no built-in duplicate finder as of October 2026. QNAP's own blog suggests jdupes, an unofficial command-line tool installed over SSH. Other options are a desktop duplicate finder pointed at a mapped share, or a NAS helper that hashes files on the device. Remove copies through File Station so they land in @Recycle.

Does ZFS deduplication remove duplicate files?

No. ZFS deduplication stores identical data blocks once, so duplicates take less space on disk, but every copy stays in its folder. It doesn't list duplicate files, and TrueNAS says it needs enough RAM to hold the dedup table and wastes resources when data isn't heavily duplicated.

Is it safe to delete duplicate files on a NAS?

Yes, if the copies are confirmed identical by content and they go to the recycle bin rather than being deleted permanently. Take a snapshot first, check that the share's recycle bin is enabled, and ask before removing a copy that someone's shortcut, mapped drive or linked spreadsheet points at.

Which copy of a duplicate file should I keep on a NAS?

Usually the oldest, because it's the original and the one existing links point to, or the one in the folder that matches your structure. Avoid keeping copies in personal, Downloads or "Old server" folders. For identical files, "newest" means nothing changed, so it's rarely the right rule.

Start with one share and the biggest groups, since that's where the space is. Run Storage Analyzer if you're on Synology, confirm by content, and remove into the recycle bin. To do it in a sentence with a plan to approve, pair your NAS with The Drive AI and ask for the duplicates on one share.