Hardware: HP DVD Writer dc300
Interface: USB
relevant output from dmesg: 
usb0: <Intel 82371AB/EB (PIIX4) USB controller> on uhci0
usb0: USB revision 1.0
uhub0: Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
uhub1: Hewlett Packard product 0x0a07, class 9/0, rev 2.00/0.00, addr 2
uhub1: 3 ports with 1 removable, self powered
ugen0: Hewlett Packard product 0x0907, rev 2.00/0.00, addr 3
umass0: Hewlett-Packard dc3000, rev 3.00/0.00, addr 4
umass0: Get Max Lun not supported (STALLED)
[...]
At the time, when the Hardware should get the "cd0" device, dmesg 
shows only the following output:
umass0: Phase Error, residue = 0
umass0: Phase Error, residue = 0
umass0: Phase Error, residue = 0
umass0: Phase Error, residue = 0

Summary:
There is no "cd0" device and the USB DVD-RW is unusable.

Fix: Edit or patch the File /usr/src/sys/dev/usb/umass.c at line 1627 with the
new line:
#if 0 /* XXX */  
and at line 1630 with the new line 
#endif 

Here is the diff:
------------------------------



+#if 0 /* XXX */
                        umass_bbb_reset(sc, STATUS_WIRE_FAILED);
                        return;

+#endif
                } else if (sc->transfer_actlen > sc->transfer_datalen) {
                        /* Buffer overrun! Don't let this go by unnoticed */
                        panic("%s: transferred %db instead of %db",

-----------------------------------------

After patching, recompiling the kernel and reboot, I've got this dmesg output:
cd0 at umass-sim0 bus 0 target 0 lun 0
cd0: <HP DVD Writer 300c 9k04> Removable CD-ROM SCSI-0 device 
cd0: 1.000MB/s transfers

and all works perfectly for me. 

Maybe only a workaround for my hardware and not a regular patch.--QeRmcCaH53OjTOSb1OczMcD9ZrQhLOGp6AtD4KwFcQ82hZbP
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--- umass.c     Thu Oct 28 09:01:15 2004
+++ umass.c_new Sun Jan  2 23:27:32 2005
@@ -1624,10 +1624,10 @@
                } else if (sc->csw.bCSWStatus == CSWSTATUS_PHASE) {
                        printf("%s: Phase Error, residue = %d\n",
                                USBDEVNAME(sc->sc_dev), Residue);
How-To-Repeat: By reboot or plug out/in there is always no success and the same error
message. Also by "camcontrol -rescan" the problem is repeatable.