[KVM/Qemu] Pass through partition with libvirt?

I'm trying to pass through a partition to my Windows-VM and followed my own thread.
I've added a storage-pool in the directory where the partition is mounted and then added the partition via livbirt-manager by-uuid as a SCSI-disk. The partition is shown under Windows, but appears to be empty, even though there are files on it, when checking under Linux. I've tried this with the partition mounted and unmounted on my host, I've tried SCSI and SATA and also by-id and by-uuid - nothing worked.
What am I missing?

You probably should never mount a filesystem on the host which you plan to use as passthrough in a vm while this vm is running.
Is there a windows-readable filesystem on that partition?
Does a linux guest (live iso, whatever) correctly see and mount your passed through partition?

I just passed through the whole disk by-id containing the NTFS-partition I tried to pass through and another ext4 partition and it just worked. What is going on?

To specify things, I usual have a drive mounted on the host, that I then pass through to the guest without a problem. I know it's not ideal, but I'm also not handling valuable data. The disk just seems to be forced to be unmounted on the host and then gets passed through.

So the question remains, why can I pass through the whole disk and not just one of the two partitions? Right now it's worked by passing the whole ("raw") disk via SCSI.

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