odd USB stick with two disks

got an odd USB stick as transport medium for an annual report. Shows up as one USB device, with two disks (SCSI sub-units), one partition each. On one disc is a read-only partition with report, the second disc is R/W for standard use. A bit odd, but whatever. Log of plugging the stick in:

log

kernel: usb 1-1.2.1.3: new full-speed USB device number 16 using ehci-pci
kernel: usb 1-1.2.1.3: not running at top speed; connect to a high speed hub
kernel: usb 1-1.2.1.3: New USB device found, idVendor=058f, idProduct=6387
kernel: usb 1-1.2.1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
kernel: usb 1-1.2.1.3: Product: Mass Storage
kernel: usb 1-1.2.1.3: Manufacturer: Generic
kernel: usb 1-1.2.1.3: SerialNumber: 77C39100
kernel: usb-storage 1-1.2.1.3:1.0: USB Mass Storage device detected
kernel: scsi15 : usb-storage 1-1.2.1.3:1.0
mtp-probe: checking bus 1, device 16: "/sys/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2.1/1-1.2.1.3"
mtp-probe: bus: 1, device: 16 was not an MTP device
kernel: scsi 15:0:0:0: Direct-Access     Generic  Flash Disk       8.08 PQ: 0 ANSI: 2
kernel: scsi 15:0:0:1: Direct-Access     Generic  Flash Disk       8.09 PQ: 0 ANSI: 2
kernel: sd 15:0:0:0: Attached scsi generic sg3 type 0
kernel: sd 15:0:0:1: Attached scsi generic sg4 type 0
kernel: sd 15:0:0:0: [sdc] 4100864 512-byte logical blocks: (2.09 GB/1.95 GiB)
kernel: sd 15:0:0:1: [sdd] 25856 512-byte logical blocks: (13.2 MB/12.6 MiB)
kernel: sd 15:0:0:0: [sdc] Write Protect is off
kernel: sd 15:0:0:0: [sdc] Mode Sense: 03 00 00 00
kernel: sd 15:0:0:1: [sdd] Write Protect is on
kernel: sd 15:0:0:1: [sdd] Mode Sense: 03 00 80 00

lsusb -v

Devices shows up with lsusb as: Bus 001 Device 011: ID 058f:6387 Alcor Micro Corp.

Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0x058f Alcor Micro Corp.
  idProduct          0x6387 Flash Drive
  bcdDevice            1.04
  iManufacturer           1 Generic
  iProduct                2 Mass Storage
  iSerial                 3 77C39100

PCB front and back side

data on USB chip by its manufacturer

Current web page at Alcor Micro, with similar chip AU6998SN (probably a successor) : http://www.alcormicro.com/en_content/c_product/product_02b.php?CategoryID=3&IndexID=13
They mention a patented in-system programming, which can probably do away with the two-disk config, via USB. However, no further details in English language seem to be available from them publicly.

8 August 2014, text and images are under the GNU_Free_Documentation_License.