USB SSD hangs on Linux

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The issue

I bought a new 250G ssd that I wanted to use as data backup. After plugging it in, I wanted to run

    sudo fdisk /dev/sdc

to format it and create a 32G partition. Unfortunately, the fdisk command would either hang right then and there or at a later stage when I tried to write out the partition with the w command.

The cause

The cause turned out to be the UAS protocol. Hard drive manufacturers often do not implement it correctly and the uas Linux kernel module is then unable to communicate with the hard drive properly.

The solution

Diagnostics

First, let us verify that the issue has to do with the uas module:

Unplug the usb ssd, run

    journalctl --dmesg --follow

and then plug it in. In my case, one of the messages was kernel: scsi host4: uas, which indicates that the uas module is in effect. Moreover, I got

kernel: usb 2-2: Product: SSD-PGU3-A
kernel: usb 2-2: Manufacturer: BUFFALO

Now run lsusb to obtain the ID of the ssd:

Bus 002 Device 002: ID 0411:02d0 BUFFALO INC. (formerly MelCo., Inc.) SSD-PGU3-A

The part we are interested in is given above by 0411:02d0. Set a temporary shell variable,

    ID=0411:02d0

On a permanent environment

If you are trying to fix this issue on a permanent environment, use

    echo options usb_storage quirks=$ID:u | sudo tee -a /etc/modprobe.d/usb_storage.conf

Then, the instructions to initrd need to be updated, so that it loads the module with the quirk. This depends on the distribution; on Debian-based distributions you would use sudo update-initramfs -u and on Fedora you would use sudo dracut -v -f. Do not blindly use these commands, it won’t work; read the manual to see exactly what it is you need to do.

In theory, initrd only needs to load the modules required to access the root filesystem. Some distributions put all common kernel modules to be loaded in initrd; there’s also udev involved which may load additional modules. As a consequence the modules are loaded before the quirk, and that’s why a new initramfs has to be generated.

On a live environment

On a live environment, such as a liveCD, use instead

    echo $ID:u | sudo tee /sys/module/usb_storage/parameters/quirks

Conclusion

What we did was inform the usb_storage kernel module that when handling the usb device with id $ID, it should not load up the uas module. The UAS protocol is useful because it is a standarized and efficient way to communicate with a usb hard drive. When manufacturers do not follow the UAS protocol, the only hope is that the uas module developers have created patches for the specific mishandling of the manufacturer. Otherwise, we have to disable the uas module for the specific device and default to USB Mass Storage, which is slower.