(Question/Issue) Constant C/OS disk writing while seeding from other disk

[QBForumAccount]

Windows 10
qB 4.6.7 (Was 5.0.1, Issue was worse, so downgraded)

I'm unaware if this is intended behaviour, but while seeding from disk D, C (OS) is constantly being written to, which is somewhat troublesome because it's an SSD, and eventually fills up with empty "used" space, which I can clear/reset if I sleep/restart the computer (File explorer claims space is used, however TreeSize can't locate anything). The amount written seems to match with amount read
Everything being seeded is located on disk D
I've tried turning off OS cache (Read and Write), turning off disk cache, converting to portable launching from disk D (Was for sure portable because resuming or pausing caused a large amount of D disk usage), however nothing seems to have fixed it, though messing with disk cache lowered disk D usage as I've turned on piece affinity and changed disk queue size to disk D's buffer size

This happens when seeding, and if left unchecked for a while will eventually fill C drive up, 5.0.1 caused smart storage from windows to activate because there was only 30G left from 250G free. I don't remember this directly happening before 5.0.1 but I do remember I would sleep the computer occasionally, my guess is it's cache but not clearing properly so it doesn't fill up entirely, 5.0.1 seemed to do it too often/worse, not sure

tl;dr
Seed from disk D, disk C writes amount seeded, written uses C disk space, file explorer claims space used, Treesize does not, sleeping/restarting computer resets used space. Tried turning off OS cache, disk cache portable mode, still writes. Not sure why/if this is intended

Sorry if my thoughts seem incoherent, if someone could clarify if this is the intended behaviour I'd appreciate it very much

[Peter]

Download the latest version, lt20 variant.
Go into advanced and and look for Disk I/O Type.
Put it "Simple pread/pwrite."

Hope it helps.
More info: https://github.com/qbittorrent/qBittorrent/pull/21300

[QBForumAccount]

Thanks, I'll leave it running for a bit and see if it's fixed,
as a side note dark mode seemed to disappear, even with "WindowsArguments = darkmode=2", but I was able to make it work by setting style (in behaviour) to "Fusion" instead of "System"

I'll reply or edit this post in near future

[QBForumAccount]

Doesn't seem to have fixed it, instead now spikes appear in usage, used space still decreases, and TreeSize still doesn't detect any used space
I'm running portable on disk D with simple pread/pwrite in advanced as disk I/O type
Pic is disk C (OS, SSD)
EDIT: Something unrelated was causing those spikes, however used space still decreased

[Peter]

It's not like I am lazy just no clue. But hey, check out these steps by your friendly fresh-water-wasting ChatGPT! The temp folder idea seems worth checking out and also the chkdsk. I've seen similar behavior when the filesystem is messed up.

This is not typical or intended behavior. It sounds like your qBittorrent configuration or a system-level caching mechanism is causing temporary files or cache to be written to the C: drive despite your torrents being seeded from the D: drive. Here are some steps to troubleshoot and possibly resolve the issue:

1. Verify Cache Configuration in qBittorrent

Go to Tools > Options > Advanced:
Ensure Disk cache is properly configured. If you disabled it entirely, try setting it to a fixed value (e.g., 512MB or 1GB) to see if it behaves differently.
Check if OS cache is enabled or disabled. You may need to experiment with toggling these settings, even though you've already tried them.

2. Check the Temp File Directory

qBittorrent might be using the C: drive as a temporary file storage location.
In Tools > Options > Downloads, verify the Temporary folder setting. If it's on the C: drive, change it to a directory on the D: drive.
Ensure "Keep incomplete torrents in a separate folder" is unchecked or points to the D: drive.

3. Investigate Windows Page File Usage

If your system is using the page file extensively during seeding, the C: drive might be written to due to virtual memory.
Check the page file settings:
Go to System Properties > Advanced > Performance > Settings > Advanced > Virtual memory.
Set the page file size manually or move it to the D: drive.

4. Analyze the "Phantom" Space Usage

Since TreeSize doesn't find the files, it's possible that the writes are to hidden or system-protected directories, or temporary files.
Use tools like Resource Monitor (Disk tab) or Process Monitor (Procmon) to track qBittorrent's disk activity. Focus on writes to the C: drive and identify the files/directories being written to.
Check the Windows Temp folder (C:\Windows\Temp) for large files or excessive activity.

5. Check for System-level Cache Behavior

Windows Disk Write Caching or a third-party tool might be interfering.
Open Device Manager > Disk Drives > Properties > Policies and adjust the Write Cache Settings for both drives.
Test whether disabling or enabling "Turn off Windows write-cache buffer flushing" affects the behavior.

6. Revert to an Older Stable Version of qBittorrent

If the issue started with version 5.0.1 and persists with 4.6.7, consider reverting further back to an earlier stable release (e.g., 4.4.x) and testing.
Sometimes newer versions introduce bugs or regressions, especially with changes to disk I/O handling.

7. Perform Disk Health Checks

Ensure there are no underlying issues with your drives:
Run chkdsk /f on both drives.
Use tools like CrystalDiskInfo to check the health of your SSD and HDD.

8. Check System Logs

Open Event Viewer and look for disk-related warnings or errors under Windows Logs > System.
Look for messages about write failures, cache issues, or low disk space warnings related to the C: drive.

9. Test with Another Torrent Client

If nothing resolves the issue, test with another torrent client (e.g., Deluge or Transmission) to confirm whether the problem is specific to qBittorrent or a broader system issue.

By systematically working through these steps, you should be able to identify whether the problem is rooted in qBittorrent, Windows caching behavior, or another system-level interference. Let me know if you'd like guidance on any specific step!

[QBForumAccount]

Update!
Sorry for having to put up with me, however thanks for doing it anyway
I found out my VPN has been logging a ton, I used Process Monitor to see writes and sure enough
Answer: Not qB, VPN

[Peter]

That is wild. Contact their support and ask WTF is it doing. Why the hell would it even write/read anything? The only actual real data a VPN client ever has to save/read is the user config.

That's weird..