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Workaround for using UAS USB3 storage on Linux

#linux #cli #tutorial

Some USB-to-SATA/NVMe bridge chips advertise UAS (USB Attached SCSI) but behave poorly under the uas driver (random I/O errors, resets, disconnects, poor SMART pass-through, etc.). A common workaround is to apply a usb-storage quirk so the device uses the classic usb-storage driver instead of uas.

This guide covers:

  • How to find the Vendor ID (VID) and Product ID (PID)
  • How to apply quirks temporarily via sysfs
  • How to apply quirks persistently via modprobe.d
  • How to specify multiple devices
  • What the quirk flags u and m mean
  • When you may need to rebuild initramfs (dracut / update-initramfs)

Identify Storage 

lsusb -tv
# view USB tree and the kernel driver in use (uas vs usb-storage)
# view VID:PID
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Tip: lsusb -tv is the easiest way to confirm which driver the kernel actually bound to the device.

Quirk Flags (What u and m mean)

The usb-storage module accepts a quirks= parameter containing one or more entries in the form:

VID:PID:FLAGS
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Common flags include:

  • u = IGNORE_UAS
    Forces the kernel to avoid binding the uas driver for this device and use usb-storage (BOT) instead.

  • m = MAX_SECTORS_64
    Limits transfer size to 64 sectors (32KB). This can improve stability for devices/bridges that misbehave with larger transfers (at the cost of performance).

A frequently used combination is mu: disable UAS and cap transfer size for stability.

Temporary Settings (runtime / non-persistent)

Writing to sysfs updates the currently running kernel only. It will be lost on reboot.

Single device 

echo "0bc2:231a:u" | sudo tee /sys/module/usb_storage/parameters/quirks

# disconnect and reconnect
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Multiple devices (comma-separated)

Use a single line with comma-separated entries:

printf '0bc2:231a:u,6795:2756:mu\n' | sudo tee /sys/module/usb_storage/parameters/quirks

# disconnect and reconnect
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Notes:

  • Use commas, no spaces.
  • This overwrites the current value (it does not append).

Add a device without losing existing entries

Because sysfs does not support append mode, read the current value, add your entry, and write it back:

cur=$(cat /sys/module/usb_storage/parameters/quirks)
new='0bc2:231a:u'

if [ -z "$cur" ]; then
  printf '%s\n' "$new" | sudo tee /sys/module/usb_storage/parameters/quirks >/dev/null
else
  printf '%s,%s\n' "$cur" "$new" | sudo tee /sys/module/usb_storage/parameters/quirks >/dev/null
fi

# disconnect and reconnect
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Persistent Settings (recommended)

To make the quirk survive reboots, set it via modprobe.d.

Create e.g. /etc/modprobe.d/usb-storage-quirks.conf:

options usb-storage quirks=0bc2:231a:u,6795:2756:mu
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Then reboot, or reload modules (reboot is typically simplest and most reliable for USB storage bindings).

initramfs note (dracut / update-initramfs)

In many cases, adding the modprobe.d file and rebooting is sufficient.

However, if your system loads storage drivers early from initramfs (for example, booting from USB storage, or using LUKS/LVM on the affected device), the new modprobe.d settings may not be applied during early boot unless you rebuild initramfs.

RHEL/CentOS/Rocky/Alma/Fedora (dracut) 

sudo dracut -f
sudo reboot
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Debian/Ubuntu (initramfs-tools) 

sudo update-initramfs -u
sudo reboot
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Notes:

  • grub2-mkconfig is typically not required for modprobe.d changes (it is for GRUB menu/kernel command-line changes, not module option files).
  • Even after rebuilding initramfs, you may still need to disconnect/reconnect the device (or reboot) so the driver binding is re-evaluated.

Confirm

Confirm the device is using usb-storage (not uas):

lsusb -tv
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Look for a line indicating something like Driver=usb-storage for your device path.

ref

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