Have you ever seen qBittorrent download a piece, throw it away, and download it again, over and over?
Or maybe a finished torrent fails its check, and you see a few percent of the data go missing.
That is what people call a hashing error. It means that a piece of the file did not match the fingerprint stored in the torrent, so qBittorrent decided the data was bad and rejected it.
In this guide, we’ll explain what a hashing error is in qBittorrent, why pieces fail the check, how to tell whether the cause is the swarm, your computer, or your drive, and how to fix each case. We’ll also show how to make qBittorrent repair a damaged torrent without downloading everything again.
What Is a Hashing Error in qBittorrent?
Every torrent is split into pieces. Each piece has a hash, which is a short code calculated from the piece’s data. The torrent file stores the hash of every piece.
When qBittorrent receives a piece, it calculates the hash of what it received and compares it to the hash in the torrent. If the two match, the piece is good and is kept. If they do not match, the piece failed the hash check and is thrown away, and the client asks for it again.
The standard torrent format uses SHA-1 hashes. Version 2 of the format, which libtorrent supports, uses SHA-256. The idea is the same in both.
So a hashing error is not a single message. It describes a group of situations where data fails this comparison: during download, during a recheck, or when the torrent finishes.
Is a Hashing Error Always a Problem?
No. A few failed pieces now and then are normal and do not mean your computer is broken.
Here is how to judge it.
- A small number of failed pieces during a download is normal. Peers sometimes send bad data by mistake, and the hash check catches it. You may see the Wasted value rise a little in the General tab.
- Repeated failures on many pieces, or failures on pieces you already had, are not normal. They point to a problem with your computer or drive.
- A torrent that fails a recheck after it was complete is a clear warning. Files changed or were damaged after they were written.
The check exists to protect you. It is better for qBittorrent to reject a bad piece than to accept it and give you a broken file.
Where Do You See Hash Failures?
You can find signs of the problem in a few places.
- The General tab: look at the Wasted value near the download amount. Wasted data includes pieces that failed the hash check and other duplicate data.
- The Execution Log: open View, then Log. Warnings about failed pieces or files appear here.
- The torrent status: after a recheck, a complete torrent may drop to 98 or 99 percent, which shows that some pieces failed.
- The pieces bar: select a torrent and look at the progress bar in the General tab. Missing pieces appear as gaps.
If your torrent sits near the end and does not finish, read our guide on how to fix a torrent stuck at 99.9 percent, because hash failures are one of the reasons for it.
Why Do Pieces Fail the Hash Check?
The causes fall into four groups: the swarm, your memory, your drive, and other software.
Bad data from a peer
Some peers send bad pieces. It can be a peer with a bad drive, faulty memory, or a broken client, or someone who sends bad data on purpose. This is the most common cause during an active download.
qBittorrent, through libtorrent, keeps track of which peers sent bad pieces and can ban a peer that sends too many. This is why you may see a few failures and then no more.
Faulty RAM
Data passes through your computer’s memory before it reaches the drive. If the memory is faulty, a bit can flip and a good piece becomes a bad one. The result is a piece that fails the check even though the peer sent correct data.
Faulty or unstable memory is a frequent cause when many pieces fail from different peers. Memory that is overclocked, or running with an XMP or similar profile that is not stable, is a common reason.
A failing drive or bad sectors
If your drive cannot store or return data correctly, files change after they are written. You may see a piece pass the check at download time and fail later at a recheck. That pattern points strongly to the drive, the cable, or the controller.
Other software touching the files
Some programs change files they should not touch.
- An antivirus may quarantine, clean, or rewrite part of a file.
- A cloud sync tool may change files while they are being written.
- A file renamer, media tool, or tag editor may edit a file inside the torrent folder.
- A copy that stopped part way may leave a file with the right size but wrong data.
Mixing up files
If you replace a file with a different version of the same name, the hash will not match. The same happens if you point a torrent at a folder that has a similar file from another release.
Unstable connections and poor networks
The network itself rarely causes bad pieces, because the protocols that carry the data check their own errors. A network problem normally causes a slow or stalled download instead of corrupted data. If failures appear on a clean connection, look at memory and the drive first.
qBittorrent Hashing Error: Quick Checks
Before you test hardware, try these.
- Look at the Execution Log for I/O errors, access denied messages, or missing files. A hash failure can come from a write that did not complete. Our guide on how to fix qBittorrent I/O error on Windows covers those.
- Check whether the failures are limited to one torrent or appear in all torrents. A single torrent suggests a bad source. All torrents suggest your computer.
- Check whether the problem started after you changed hardware, installed a new antivirus, or changed memory settings.
- Check free space on the drive.
How to Fix qBittorrent Hashing Error
Step 1: Force recheck the torrent
Right-click the torrent and choose Force recheck. qBittorrent reads every file and compares each piece to the torrent. Pieces that match stay. Pieces that fail become missing, and the client downloads them again.
This is the main repair tool. It lets you fix a damaged torrent without starting from zero. If the recheck ends with the torrent complete, the earlier failure was a temporary problem.
Step 2: Let qBittorrent download the missing pieces
After the recheck, resume the torrent. If there are seeds, the missing pieces download and the torrent completes. If the same pieces fail again, check the next steps.
Step 3: Check whether the same pieces fail again
If new downloads fail the check each time, compare the General tab values. If the Wasted value grows quickly, a lot of pieces are being rejected.
One bad peer is not the same as a bad computer. Look at the Peers tab and see whether the flagged peers disappear after a short time. If failures continue with new peers, suspect your own system.
Step 4: Test your memory
Memory problems often show up as hash failures before they cause crashes.
- On Windows, press the Windows key, type Windows Memory Diagnostic, and run it. It restarts the computer and runs a test.
- For a deeper test, use MemTest86 from a USB drive. It runs outside Windows and can find errors that the basic test misses. Let it run for several passes.
If the test shows errors, remove memory sticks one at a time to find the faulty one. If you overclocked your memory, turn off XMP or similar profiles and return to default settings. If the failures stop, the profile was unstable.
Step 5: Scan and check the drive
Run a file system check and look at the drive health.
- Right-click the drive in File Explorer, choose Properties, Tools, then Check. Or run chkdsk with the /f option from an administrator Command Prompt.
- Open a drive health tool and look at SMART data. Reallocated sectors, pending sectors, or failed health status mean you should replace the drive.
- Try another cable or port for external drives. A weak connection can corrupt writes.
If you suspect the drive, test by downloading the same torrent to a different drive. If the failures disappear, the first drive is the cause.
Step 6: Exclude the download folder from antivirus and sync tools
Add the download folder to your antivirus exclusion list, and move it out of folders that cloud tools sync. This stops them from changing files that qBittorrent is still writing or sharing.
Step 7: Do not edit files inside the torrent folder
Leave the files as they are while the torrent is active. If you need to edit, rename, or tag a file, copy it to another folder first. Otherwise the next recheck will find that the data does not match.
Step 8: Update qBittorrent
Older versions can contain bugs in disk handling. Install the latest stable version from the official website and restart the computer.
Step 9: Check the source
If everything on your side looks fine, the torrent itself may be a poor source. Some torrents have bad pieces in the swarm that nobody can fix, for example if the original uploader’s files were damaged. In that case, no setting helps. Look for another source from an official website, or find a different torrent for the same file.
What Does the Recheck on Completion Option Do?
qBittorrent has an option to recheck torrents on completion. It is in the Options window, and when it is on, qBittorrent verifies every piece as soon as a download finishes.
This adds extra disk work, and for most users it is not needed, because pieces are already checked as they arrive. It can be useful if you suspect your system is writing data badly, because it confirms that what is on the drive matches the torrent. If you turn it on, expect each completed torrent to spend some time in the Checking state.
Can a Hashing Error Damage Files I Have Already Finished?
Hash checks do not damage files. They only read them. But the problems that cause hash failures, such as bad memory or a failing drive, can damage files, and the check is how you find out.
If a torrent that was complete fails a recheck, you have learned that the data on your drive changed. Do not seed it until you repair it, because you might share bad pieces. Recheck, let the missing pieces download, and then continue.
Hybrid and Version 2 Torrents
Some torrents are hybrid, which means they contain both SHA-1 and SHA-256 hashes so older and newer clients can use them. Newer versions of qBittorrent, built on libtorrent 2, support these. Hash checks on these torrents work the same way, and the repair steps do not change.
If a torrent fails to load or check in an old client, update the client. Older clients may not read the version 2 data correctly.
How to Tell Whether the Problem Is Bad Peers or Bad Hardware
This table in words can help you decide.
- Few failures, all from one or two peers, and they stop: normal. A peer sent bad data and was banned.
- Many failures across many peers, on many torrents: suspect memory or the drive.
- Failures only on one torrent, but clean on others: suspect that torrent’s source.
- Failures that appear only after a recheck of a completed torrent: suspect the drive, other software, or changed files.
- Failures that began after you changed memory settings or overclocked: suspect that change.
- Failures on one drive only: suspect that drive or its cable.
You can use this list as a map. It tells you which test to run first.
Common Mistakes When Fixing Hashing Errors
- Deleting the torrent and the files at once. A recheck is faster and keeps the good data.
- Ignoring the memory test. Many users change qBittorrent settings for hours when the memory was the cause.
- Running the recheck before fixing a failing drive. The recheck itself will pass over bad sectors and the same pieces may fail again.
- Editing files in the torrent folder. Even a small change breaks a piece.
- Assuming the client is broken. The check is working as designed.
- Trusting a skip hash check option to fix a problem. Skipping the check hides the issue and does not repair data.
How to Prevent Hashing Errors
- Use stable memory settings, and test new memory before you rely on it.
- Keep your drive healthy and watch its SMART status.
- Keep the download folder out of synced and scanned locations, or add exclusions.
- Do not move, rename, or edit active torrent files.
- Safely eject external drives and avoid unplugging them during a download.
- Keep the computer plugged in and avoid power loss during writes.
- Keep qBittorrent and your drivers up to date.
How Pieces, Blocks, and Hashes Fit Together
It helps to know how big the units are, because it explains why a small error can waste a lot of data.
A torrent is divided into pieces. The piece size is chosen by whoever made the torrent, and it commonly ranges from 256 KiB to 16 MiB or more for large torrents. You can see the piece size in the General tab of qBittorrent, in the Information section.
Pieces are downloaded in smaller blocks, usually 16 KiB each. Different peers may send different blocks of one piece. qBittorrent assembles all the blocks, calculates the hash for the whole piece, and only then compares it with the torrent.
This has an important result. If one block inside a piece is bad, the whole piece fails. With a 4 MiB piece, one bad block means qBittorrent has to download the full 4 MiB again. That is why a small number of bad blocks can raise the Wasted value quickly, especially on torrents with large pieces.
What Happens When qBittorrent Finds a Bad Piece?
The process is simple.
- qBittorrent compares the piece hash and finds a mismatch.
- It discards the piece and marks it as missing.
- It notes which peers sent blocks for that piece.
- It requests the piece again, often from different peers.
- If a peer is linked to repeated failures, libtorrent can ban it for the session.
You do not need to do anything for this process to work. It happens in the background. You only need to act if failures are frequent or keep coming back.
How to Ban a Peer That Sends Bad Data
If you can see a specific peer that keeps sending bad data, you can ban it yourself.
- Select the torrent and open the Peers tab.
- Right-click the peer and choose Ban peer permanently.
- Confirm when qBittorrent asks.
A permanent ban stays in place across restarts. You can review or clear banned addresses in Tools, Options, Connection, under the IP filtering or banned IP list, depending on your version. Do not ban many peers at random. A healthy swarm needs peers, and a ban on a good peer slows your download.
Example Situations and What They Mean
Example 1: A new download wastes a little data
You add a torrent and, near the end, the General tab shows a small Wasted value. The torrent completes and passes a recheck. This is normal. A peer sent a bad block, qBittorrent threw the piece away, and it downloaded the piece again.
Example 2: A finished torrent drops from 100 percent to 97 percent after a recheck
You moved the files with a file manager, then asked qBittorrent to check. Some pieces failed. This can happen if the copy did not finish, if a file was edited, or if the drive returned bad data. Recheck again after confirming the copy is complete. If the same pieces fail, test the drive.
Example 3: Every torrent shows failures
Failures on many unrelated torrents point to your computer. Test the memory first, then the drive. If you changed memory settings recently, undo them.
Example 4: Only one torrent has trouble
If other torrents are fine and one keeps failing, the source may be faulty. Try a fresh copy of the torrent from the original site, or choose another release of the same content.
Example 5: A torrent fails only after an antivirus scan
The scanner may have cleaned or replaced part of a file. Restore the file from quarantine if it is a false positive, add an exclusion, and recheck.
How to Run a Proper Memory Test
Memory errors can be rare and random, so a short test may miss them. A better routine is:
- Create a MemTest86 USB drive from the official site and boot from it.
- Run at least four passes, and more if you can leave the computer overnight.
- If any error appears, the memory or its settings are unstable.
- Test each stick alone, in the same slot, to find the bad one.
- Return the BIOS memory settings to defaults and test again.
If the memory passes cleanly but failures continue, test the drive next. Do not skip the drive just because the memory is fine.
Reading Drive Health in Simple Terms
Drives report health through SMART data. You can read it with a free tool or the drive maker’s own program. These values matter most for a hard drive:
- Reallocated sector count: the number of bad sectors the drive replaced. A rising number is a warning.
- Current pending sector count: sectors waiting to be checked. A non-zero value that stays is a warning.
- Uncorrectable sector count: sectors the drive could not read.
For SSDs, look at the percentage of life used, the media errors, and any warning flag the tool shows. If the drive passes these checks, look at the cable, port, and controller instead. For Linux users, the smartctl command from the smartmontools package prints the same information from a terminal.
What to Do If You Cannot Find the Cause
Sometimes every test passes and failures still appear. Try this order:
- Update the BIOS and the chipset and storage drivers.
- Test with a different drive or a different computer, if you can.
- Download a healthy, popular torrent, such as an official Linux image, to the same folder. If it also fails, the system is at fault. If it passes, the original torrent is the problem.
- Switch off all overclocking and run with default settings for a day.
- Keep a short note of when failures happen. A pattern, such as only when the computer is warm or busy, points to heat or power.
Heat is a real cause. A computer that runs very hot can produce memory or drive errors. Clean dust from fans, check temperatures, and improve airflow.
Do Not Seed Damaged Data
If a recheck shows a torrent is damaged, pause it before you seed. Peers that receive a bad piece from you will see the hash failure, and some may ban you. Repair the torrent first, then resume. Our guide on how long you should seed a torrent covers what to do once the torrent is healthy again.
When Skip Hash Check Is the Right Choice
When you add a torrent in qBittorrent, there is an option to skip the hash check. It tells the client to trust the existing files and move straight to seeding.
Use it only if you are certain the files are complete and correct. A good example is moving a finished torrent to a new drive, where you copied the files and want to start seeding without a long check. Do not use it to hide errors. If the files are damaged, skipping the check means qBittorrent may seed bad pieces. Our guide on how to move torrents to another drive without downloading again shows the safe way to do this.
Frequently Asked Questions (FAQs)
What does a hashing error mean in qBittorrent?
It means a piece of data did not match the hash stored in the torrent, so qBittorrent rejected it. The client then asks for the piece again.
Is a hash check failure dangerous?
No. The check protects you from bad data. A few failures are normal. Many failures point to a problem with memory, the drive, or other software.
Why does my completed torrent fail the recheck?
Files changed after they were written. The cause can be a failing drive, an antivirus that changed a file, an edit to a file, or an unfinished copy. Force recheck and let qBittorrent download the missing pieces.
How do I fix a torrent with hash errors without starting again?
Use Force recheck. It keeps the good pieces and marks the bad ones as missing. After that, resume the torrent so it downloads only what is missing.
Can bad RAM cause hashing errors in qBittorrent?
Yes. Faulty or unstable memory can change data before it reaches the drive. Run Windows Memory Diagnostic or MemTest86, and turn off memory overclocking to test.
Can antivirus cause hash failures?
It can. If an antivirus cleans, quarantines, or rewrites part of a file, the pieces no longer match. Add the download folder to your exclusions.
Why do the same pieces keep failing?
If new peers keep sending data that fails the check, suspect your own computer. If the torrent itself has bad pieces in the swarm, no setting can fix it, and you should look for another source.
Does skip hash check fix the error?
No. It tells qBittorrent to trust the files without verifying them. It hides the problem, and bad pieces can remain. Use it only when you know the files are correct, for example after moving a finished torrent.
What is the Wasted value in qBittorrent?
It is the amount of downloaded data that was not used, mainly pieces that failed the hash check or arrived as duplicates. A small amount is normal. You can see it in the General tab.
How often should I recheck my torrents?
You do not need to do it on a schedule. Recheck when you suspect damage, after a crash or power loss, after moving files, or when a completed torrent behaves oddly. Our guide on why qBittorrent keeps rechecking torrents explains when checks happen on their own.
Final Thoughts
A hashing error is qBittorrent doing its job. It compared the data against the torrent and found a mismatch.
A few failed pieces from a bad peer are normal. Repeated failures, or a finished torrent that fails a recheck, are signs to check your memory, your drive, and any software that touches the files.
The best repair tool is Force recheck. It keeps the good data, finds the bad pieces, and lets qBittorrent fetch only what is missing. If the same problem returns, test the memory and the drive before you change more settings.
