Tested guest OS: Fedora 22 Ubuntu 14.04 USB HDD is formatted as NTFS/exFAT/ext4. Reproduction steps: 1. Plug USB HDD 2. Attach USB HDD to guest OS It's not something related to file system type, it should be something wrong in lower level. dmesg: I'll post detailed when I'm back home. I only remember that there is an error like "not accepting adress", "timeout", or an error around "scsi" subsystem. Meanwhile, I have a Windows 10 guest, and USB HDD works fine. I submitted a ticket today but unfortunately it was a wasted of time, and what's more, even the problem was still unclear, state of the ticket had been changed to "RESOLVED" by someone. This made me a bit annoyed.