27 October 2011

How to enable support for multi-lun USB devices.

Damn, here was a problem. My shiny new USB smart card reader and integrated memory stick wouldn't quite work properly in Arch. The smart card reader was fine, but the mass storage device wasn't showing up. It seemed that the device had multiple LUNs (logical units), and the default Arch kernel wasn't configured to see these. No bother, we can add this to /etc/modprobe.d/modprobe.conf:

options scsi_mod max_luns=4

Then be sure to rebuild your initial RAM disk:

# mkinitcpio -p linux

And upon a reboot, the USB mass storage device is found!

(I have no idea why this functionality isn't enabled by default; perhaps there's some other problem that this can cause?)

Thanks to this article on the Adaptec knowledge base for providing the know how.

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