qBittorrent official forums

Hi.

I'm using the latest qB 5.1.0 (LT20) from PPA on Ubuntu 25.04 on my RPi 5 4GB. The RPi has a good SSD connected - Crucial MX500 1TB (with DRAM) in a USB 3.0 enclosure. This works with a 300Mbit/s FTTH (DL 37.5MB/s). My RPi works 24/7 as a seedbox/NAS.

Now, when I download a big torrent, say 100GB, after a few seconds from the start of the download, I get "write cache overload" and the download virtually stops. What I can see in Ubuntu's System Monitor is that qB constantly writes about 100 to 350MB/s to the SSD every second (but doesn't download anything at the same time). So there's a VERY unusual disk activity by qB. The actual download only starts after 1 hour or so (100GB torrent). When the torrent finally finishes downloading, I can see in System Monitor, that Total Disk Writes increased by around 200GB, but I have only downloaded a 100GB torrent, so it looks like qB has written twice the amount of data.

I have pre-allocate files disabled. I tried every combination of Disk IO type and Disk IO read/write mode - it doesn't help. I also increased qB's working set to 1GB and Disk queue size to 256000 kB - it doesn't help. I also tried a bit older qB from the official Ubuntu repo - it behaves in the same way. I tried to reformat the SSD, first to NTFS, next to exFAT - neither helped.

The only thing that helps is when I exit qB and start it again (even without OS restart). Then, immediatally after launch, it downloads fine (37.5MB/s), but the next day the problem comes back with a new torrent I try to download.

Any help appreciated.

Here's the SSD benchmark from Disk Utility:

I think the problem is solved. I reformatted the USB SSD to ext4, and since then, I downloaded 700GB+ of data at full speed of my Internet connection. No more write cache overload.

Interesting thing is, it was ChatGPT which suggested the solution. It said, that exFAT isn't optimal on Linux, because of some FUSE driver. It recommended F2FS and ext4. But F2FS isn't working on RPi5 out-of-the-box, so I chose ext4.