17.5 USB Storage Devices

Contributed by Marc Fonvieille.

A lot of external storage solutions, nowadays, use the Universal Serial Bus (USB): hard drives, USB thumbdrives, CD-R burners, etc. FreeBSD provides support for these devices.

17.5.1 Configuration

The USB mass storage devices driver, umass(4), provides the support for USB storage devices. If you use the GENERIC kernel, you do not have to change anything in your configuration. If you use a custom kernel, be sure that the following lines are present in your kernel configuration file:

device scbus
device da
device pass
device uhci
device ohci
device usb
device umass

The umass(4) driver uses the SCSI subsystem to access to the USB storage devices, your USB device will be seen as a SCSI device by the system. Depending on the USB chipset on your motherboard, you only need either device uhci or device ohci, however having both in the kernel configuration file is harmless. Do not forget to compile and install the new kernel if you added any lines.

Note: If your USB device is a CD-R or DVD burner, the SCSI CD-ROM driver, cd(4), must be added to the kernel via the line:

device cd

Since the burner is seen as a SCSI drive, the driver atapicam(4) should not be used in the kernel configuration.

Support for USB 2.0 controllers is provided on FreeBSD 5.X, and on the 4.X branch since FreeBSD 4.10-RELEASE. You have to add:

device ehci

to your configuration file for USB 2.0 support. Note uhci(4) and ohci(4) drivers are still needed if you want USB 1.X support.

Note: On FreeBSD 4.X, the USB daemon (usbd(8)) must be running to be able to see some USB devices. To enable it, add usbd_enable="YES" to your /etc/rc.conf file and reboot the machine.

17.5.2 Testing the Configuration

The configuration is ready to be tested: plug in your USB device, and in the system message buffer (dmesg(8)), the drive should appear as something like:

umass0: USB Solid state disk, rev 1.10/1.00, addr 2
GEOM: create disk da0 dp=0xc2d74850
da0 at umass-sim0 bus 0 target 0 lun 0
da0: <Generic Traveling Disk 1.11> Removable Direct Access SCSI-2 device
da0: 1.000MB/s transfers
da0: 126MB (258048 512 byte sectors: 64H 32S/T 126C)

Of course, the brand, the device node (da0) and other details can differ according to your configuration.

Since the USB device is seen as a SCSI one, the camcontrol command can be used to list the USB storage devices attached to the system:

# camcontrol devlist
<Generic Traveling Disk 1.11>      at scbus0 target 0 lun 0 (da0,pass0)

If the drive comes with a file system, you should be able to mount it. The Section 17.3 will help you to format and create partitions on the USB drive if needed.

If you unplug the device (the disk must be unmounted before), you should see, in the system message buffer, something like the following:

umass0: at uhub0 port 1 (addr 2) disconnected
(da0:umass-sim0:0:0:0): lost device
(da0:umass-sim0:0:0:0): removing device entry
GEOM: destroy disk da0 dp=0xc2d74850
umass0: detached

17.5.3 Further Reading

Beside the Adding Disks and Mounting and Unmounting File Systems sections, reading various manual pages may be also useful: umass(4), camcontrol(8), and usbdevs(8).

This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.