qBittorrent fails to download to MergerFS pool shared via SMB on OMV7

I installed OpenMediaVault 7 and created a storage pool using MergerFS. This pool is shared over the network via SMB.

I deployed qBittorrent in a Docker container and tried to download torrents directly to the MergerFS pool. The client creates the destination file in the pool, but then the download speed drops to zero and the torrent ends up in an error state. Unfortunately, I haven’t been able to find where to check the exact error message.

To troubleshoot, I also installed qBittorrent directly on the host (outside of Docker), and it behaves exactly the same—downloads stall after file creation.

However, when I point qBittorrent to a directory outside the MergerFS pool (i.e., a regular folder on a single disk), downloads work fine.

As another test, I installed Transmission in a container, and it successfully downloads to the MergerFS pool—but I prefer qBittorrent as my torrent client and Transmission doesn’t meet my needs.

Currently, as a workaround, I’ve mapped the MergerFS pool as a network drive on my Windows 11 PC via SMB and run qBittorrent locally, downloading directly to that network location. This works, but I’d really prefer a fully autonomous setup running directly on the OMV server.

Any help with configuring qBittorrent to work properly with the MergerFS pool would be greatly appreciated!

Quote from ryecoaaron

I don't use qbittorrent but there are docs about this - https://trapexit.github.io/mergerfs/latest/known_issues_bugs/#3rd-party-software
You will likely need to change some options.

Thank you!

I changed the Disk I/O type setting in qBittorrent from "Memory mapped files" to "POSIX-compliant", and now it downloads to the MergerFS pool without any issues.