On Tue, 19 Mar 2024 15:08:57 +0100
Michael Reinelt [off-list ref] wrote:

I think I found at least a workaround: the strange behaviour disappears immediately, if I disable
UAS, and use usb-storage for the externel USB drive.

options usb-storage quirks=04e8:4001:u

I am sure that UAS has been used with kernel 6.1, too, where it did not cause any issues...

Ideas what is going wrong in kernel 6.6? I'd like to re-enable UAS, because UAS is about 200 MB/sec
faster than usb-storage

I think it might be related to discard or write zeroes support on 6.6. I had
some issues enabling USB TRIM on kernel 6.6, compared to 6.1.

What do you get for "lsblk -D" on both kernels and both storage drivers on 6.6,
are there any differences?

Aside from that, trying "blktrace" was a good suggestion to figure out the
process writing or even the content of what is being written.

-- 
With respect,
Roman