Windows Copy/Paste UI Shows High Transfer Speed Compared to Task Manager Disk Activity

Question

Hi ,

I'm currently using Windows Server 2019, and I've noticed something unusual during file copy operations. I've disabled the write-caching policy on all my disks, yet when I copy a 5GB file from the C: drive to the E: drive (both in different physical HDDs, i.e. in two different partitions), the Windows copy/paste UI shows a transfer speed of 2 GB/s.

This is clearly not accurate—my HDD simply isn't capable of that speed. So I opened Task Manager during the copy process and observed that the actual write speed to the E: drive hovered around 200 MB/s, continuing for several seconds even after the copy/paste UI reported the transfer as "complete."

Screenshots:

Here's what I’ve tested/tried so far:

• After the UI reported the copy as complete, I compared both the source and destination folders in Beyond Compare. All files were present in the destination, even while Task Manager still showed ongoing disk activity.

• I found some discussions online stating that Windows may still use RAM, or other filesystem I/O for caching even when disk write caching is disabled. To test this, I ran RAMMap before and after the copy operation. However, I didn’t observe any major changes in its data.

• I did notice in Task Manager that the “Cached” memory increases during the copy and then drops after the disk activity ends.

• In Windows Server 2012 R2, this anomaly was not present, write speeds were same in File Explorer UI and Task Manager

My concerns and questions:

1. Why is the Windows copy/paste UI showing such a misleading transfer speed? This gives a false impression that the operation is complete and successful when in reality, the system is still writing to disk.
2. Is this caching behavior default in Windows Server, even with disk write-caching disabled?
3. Is there any way to completely disable all levels of caching, including memory-level buffering, so the UI accurately reflects the true disk write speed and completion status?
4. I'm particularly concerned about data integrity and loss, especially in environments where accurate reporting of file operations is critical.

Thanks in advance for any insights!