In the interests of getting around 1TB of data onto disk faster for offsite backups, we bought a PCIe USB3 adapter: lspci 16:00.0 USB controller: NEC Corporation uPD720200 USB 3.0 Host Controller (rev ff) pspci -n 16:00.0 0c03: 1033:0194 (rev ff) and also a USB3 caddy that holds bare disks. This was working great on a test machine so we moved it across to a production machine and it's being nothing but trouble. The test machine is a HP ML110G6, and the production machine is a HP ML370G5. The adapter uses the xhci_hcd module, and after it plays up and I try and unload and load the module it says: [353709.836103] xen: registering gsi 19 triggering 0 polarity 1 [353709.836113] xen_map_pirq_gsi: returning irq 19 for gsi 19 [353709.836117] xen: --> pirq=19 -> irq=19 (gsi=19) [353709.836121] Already setup the GSI :19 [353709.836125] xhci_hcd 0000:16:00.0: PCI INT A -> GSI 19 (level, low) -> IRQ 19 [353709.836204] xhci_hcd 0000:16:00.0: xHCI Host Controller [353709.836225] xhci_hcd 0000:16:00.0: new USB bus registered, assigned bus number 1 [353709.836253] xhci_hcd 0000:16:00.0: can't setup [353709.836349] xhci_hcd 0000:16:00.0: USB bus 1 deregistered [353709.836419] xhci_hcd 0000:16:00.0: PCI INT A disabled [353709.836423] xhci_hcd 0000:16:00.0: init 0000:16:00.0 fail, -19 So something has gotten stuck somewhere. I'm running debian 3.2.0-2-amd64 kernel. It seems that the USB3 caddy is no longer working as it also exhibits similar symptoms when plugged in to a USB2 port, but I've tried other USB2 and USB3 devices on the USB3 adapter and they appear to be doing similar things so now I'm not so sure. Any suggestions? Can anyone name an adapter that is working well for them? Thanks James