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[Help] TerraSync backup task stuck on 'scanning'
Posted: 25 Feb 2026, 07:06
by Clavus
I set up a Terramaster F2-425 NAS for backing up my files (around 4TB). Initially I had the NAS at my own home. The TerraSync backup task ran without issue. I recently moved the NAS to an external location, and I set it up for remote access (manually with port forwarding, reverse proxy, etc etc). That all works fine, my TNAS PC For Windows app connects without a problem. However, after setting up the new TerraSync server destination and recreating the backup task. Now whenever it runs it remains stuck on 'scanning', for over a week now. I know it's 4TB of data, but most of the files are already there from when the NAS was still in my own house. The upload / download speed should also be within the 100mbit/s range.
So did recreating the backup task or changing the terrasync server destination cause it to have to verify all the files again in a slower manner? I also sometimes have connection interruptions; does this mean the backup task has to start over?
I also have a TerraSync one-way sync task running on another folder from the NAS to the PC, and that one completes just fine. It's just the backup task that never seems to complete.
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 25 Feb 2026, 09:42
by IrisLi
We suspect the issue is caused by an unstable network connection via your remote access method.Each time the connection drops and reconnects, a full rescan is triggered automatically.
Does your connection frequently disconnect?If not, you can go to Log module → Settings, export the debug logs, and send them to our technical support email.
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 05 Mar 2026, 03:22
by Clavus
An update on my issue. I've decided to simply restart the backup process, which is going to take a while giving that it's 4TB, with about a 100 mbit connection. I decided doing it in batches by expanding the amount of folders that the backup task synchronises to see how it behaves. I find that, even with about ~500GB now synced it still tends to get stuck in long periods of 'scanning' files even when there's been no network interruption. How does the backup process work? Does it fully scan and compare file hashes every time or does it actually cache and watch for changes dynamically? Does that behaviour differ if you have it set to Instant Backup or Scheduled Backup?
I'm wondering if a one-way sync task would be a better solution when I reach the point where I backup my large media folders instead of the backup task. What is recommended in that case?
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 05 Mar 2026, 16:44
by MikeZhang
There might have been a brief network interruption during the scan, requiring it to rebuild the file list and perform a new scan to "calibrate" the status. This would manifest as a lengthy "scan" process. With your 4TB of data, this process would naturally be amplified. Your idea of a "one-way synchronization task" is perfectly suited for your scenario of backing up large media folders.
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 18 Mar 2026, 20:27
by Clavus
I've decided to rebuild part of my backup setup to see where things are causing issues. I noticed that even without any active sync or backup tasks running, the TerraSyncServer process is showing high CPU usage on the NAS:
It wasn't showing anything in the log as to what was keeping it busy.
I uninstalled the TerraSync app from my NAS, which eventually caused the device to calm down. It'd been almost consistently noisy and constantly hitting the drives up till this point.
Now a few days later I've installed the TerraSync app again to reconfigure it from the ground up. However right after installing and adding the team folders, it's right back to high CPU usage without any processes running. What could be causing this? Does the app instantly start scanning the team folders you add? Or could it be there are some lingering cache files or configuration from the previous installation that could be causing this? What folders should I make sure are removed after uninstalling?
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 19 Mar 2026, 15:14
by Phil
Clavus wrote: ↑18 Mar 2026, 20:27
I've decided to rebuild part of my backup setup to see where things are causing issues. I noticed that even without any active sync or backup tasks running, the TerraSyncServer process is showing high CPU usage on the NAS:
It wasn't showing anything in the log as to what was keeping it busy.
I uninstalled the TerraSync app from my NAS, which eventually caused the device to calm down. It'd been almost consistently noisy and constantly hitting the drives up till this point.
Now a few days later I've installed the TerraSync app again to reconfigure it from the ground up. However right after installing and adding the team folders, it's right back to high CPU usage without any processes running. What could be causing this? Does the app instantly start scanning the team folders you add? Or could it be there are some lingering cache files or configuration from the previous installation that could be causing this? What folders should I make sure are removed after uninstalling?
When you add a shared folder as a "team folder," it takes time to generate file versions. The time required to generate file versions depends on the size and number of files within the folder, and this process continuously consumes CPU and disk I/O. Therefore, high CPU usage is normal and unrelated to previously cached files. After reinstalling TerraSync, you can try adding team folders in batches: don't add all folders at once. Add the folder with the fewest files first, let it complete the initial indexing, and observe the resource usage decrease before adding the next one; alternatively, you can operate during idle periods: perform the initial addition and indexing at night or when no one is using the site.
This issue with TerraSync is also mentioned in the documentation; you can refer to this link:
https://toshelp.terra-master.com/docs/T ... /terrasync
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 19 Mar 2026, 15:55
by Clavus
Thanks for the reply. Another question then: if I then set up the sync task again and link it to a folder that already has all the same files, it will spend have to spend time syncing these again again. However I'm not sure how it goes about this process: is it actually uploading all the files again to compare? Or does it just compare file hashes, which would minimize network bandwidth? I'm asking since the last time I tried this it seemed like it was just reading all files again and uploading them.
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 19 Mar 2026, 17:47
by Phil
Clavus wrote: ↑19 Mar 2026, 15:55
Thanks for the reply. Another question then: if I then set up the sync task again and link it to a folder that already has all the same files, it will spend have to spend time syncing these again again. However I'm not sure how it goes about this process: is it actually uploading all the files again to compare? Or does it just compare file hashes, which would minimize network bandwidth? I'm asking since the last time I tried this it seemed like it was just reading all files again and uploading them.
Your analysis is correct.
When you redirect the synchronization task to a folder that already contains all the same files, TerraSync will not upload all the files again. Its core logic is "incremental synchronization," which means it only transmits the changed parts.
It uses a combination strategy of quickly scanning attributes and then accurately comparing hash values when necessary to minimize unnecessary network transmission.
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 30 Mar 2026, 05:03
by Clavus
In the end I also found out there was a corrupted sector on one of my harddrives. This caused a sync task to get stuck on 'scanning'. After exporting and checking the TerraSync PC app's debug log I found out it was repeatingly logging these messages:
9. GetFileInformationByHandleEx F:\
(filepath to corrupted folder): Incorrect function.
Stack:
1. terrasync/pkg/scanner.(*Scanner).Run
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/pkg/scanner/scanner.go:153
2. terrasync/client/synctask.(*internalTask).run.func3
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/client/synctask/synctask.go:339
3. golang.org/x/sync/errgroup.(*Group).Go.func1
C:/Users/twm/go/pkg/mod/golang.org/x/
[email protected]/errgroup/errgroup.go:93
2026-03-29 13:30:19.218 [ERRO] C:/teamcity/buildAgent/work/7956898a1ca992da/backend/pkg/scanner/scanner.go:153: 1. failed to walk dir
1). terrasync/pkg/scanner.(*Scanner).walkDirs
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/pkg/scanner/scanner.go:285
2). terrasync/pkg/scanner.(*Scanner).Run
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/pkg/scanner/scanner.go:143
3). terrasync/client/synctask.(*internalTask).run.func3
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/client/synctask/synctask.go:339
4). golang.org/x/sync/errgroup.(*Group).Go.func1
C:/Users/twm/go/pkg/mod/golang.org/x/
[email protected]/errgroup/errgroup.go:93
2. failed to walk dir
1). terrasync/pkg/scanner.(*Scanner).walkDirs
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/pkg/scanner/scanner.go:285
2). terrasync/pkg/scanner.(*Scanner).walkDirs
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/pkg/scanner/scanner.go:283
3). terrasync/pkg/scanner.(*Scanner).Run
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/pkg/scanner/scanner.go:143
4). terrasync/client/synctask.(*internalTask).run.func3
C:/teamcity/buildAgent/work/7956898a1ca992da/backend/client/synctask/synctask.go:339
5). golang.org/x/sync/errgroup.(*Group).Go.func1
C:/Users/twm/go/pkg/mod/golang.org/x/
[email protected]/errgroup/errgroup.go:93
I'd be nice if TerraSync could report back if it runs into an issue like this instead of getting stuck.
Re: [Help] TerraSync backup task stuck on 'scanning'
Posted: 30 Mar 2026, 14:37
by EriChan
Thank you for your proactive feedback! Your suggestions are very important to us. Our project team has received your input and is currently conducting an evaluation. We will prioritize improvements for this type of issue in our upcoming optimization roadmaps. If you have any further findings, please feel free to let us know at any time!