lsusb not listing a SCSI drive, connected through USB (SATA bridge)?

Question

I'm looking at one of those detachable hybrid laptops, which has extra hard drive in the keyboard base; this laptop runs Ubuntu. Sometimes these drives mount at startup, sometimes not - and in inspecting, I just noticed something that I don't understand.

So when this drive is mounted and working properly, here is the relevant output of lshw:

$ sudo lshw -businfo | grep 'disk\|volume'
scsi@4:0.0.0      /dev/sdb   disk           500GB HTS545050A7E380
scsi@4:0.0.0,1    /dev/sdb1  volume         222GiB EXT4 volume
scsi@4:0.0.0,2    /dev/sdb2  volume         222GiB EXT4 volume
scsi@4:0.0.0,3    /dev/sdb3  volume         20GiB Windows NTFS volume

With lshw -v, I get the following for this drive:

 *-scsi:1
      physical id: 2
      bus info: usb@2:1.2
      logical name: scsi4
      capabilities: emulated scsi-host
      configuration: driver=usb-storage
    *-disk
         description: SCSI Disk
         product: HTS545050A7E380
         vendor: Hitachi
         physical id: 0.0.0
         bus info: scsi@4:0.0.0
         logical name: /dev/sdb
         version: AD04
         serial: TE85313R0LU5JK
         size: 465GiB (500GB)
         capabilities: gpt-1.00 partitioned partitioned:gpt
         configuration: ansiversion=6 guid=d0ba2288-a760-46db-8675-fe22d9becf8e sectorsize=512

So, it does tell me this drive is connected somehow through USB; and that it is a Hitachi. However, when I do lsusb, it is not listed at all:

$ sudo lsusb
Bus 004 Device 005: ID 03eb:8808 Atmel Corp.
Bus 004 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 004 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 004: ID 114d:0140 Alpha Imaging Technology Corp.
Bus 003 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 003: ID 05e3:0735 Genesys Logic, Inc.
Bus 002 Device 002: ID 05e3:0612 Genesys Logic, Inc.
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 0483:91d1 STMicroelectronics Sensor Hub
Bus 001 Device 005: ID 2a47:0c02
Bus 001 Device 004: ID 05e3:0606 Genesys Logic, Inc. USB 2.0 Hub / D-Link DUB-H4 USB 2.0 Hub
Bus 001 Device 002: ID 05e3:0610 Genesys Logic, Inc. 4-port hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

In other words, no Hitachi here. System log /var/log/syslog relevant logs:

kernel: [    2.963255] scsi 4:0:0:0: Direct-Access     Hitachi  HTS545050A7E380
kernel: [    2.963490] sd 4:0:0:0: Attached scsi generic sg1 type 0
kernel: [    2.964196] sd 4:0:0:0: [sdb] 976773152 512-byte logical blocks: (500 GB/465 GiB)
kernel: [    2.966060] sd 4:0:0:0: [sdb] Write Protect is off
kernel: [    2.966063] sd 4:0:0:0: [sdb] Mode Sense: 5f 00 10 08
kernel: [    2.967007] sd 4:0:0:0: [sdb] Write cache: enabled, read cache: enabled, supports DPO and FUA
kernel: [    3.019250]  sdb: sdb1 sdb2 sdb3
kernel: [    3.021523] sd 4:0:0:0: [sdb] Attached SCSI disk
kernel: [    3.381991] clocksource: Switched to clocksource tsc

And finally I checked with udevadm info -a -n sdb; here it finds the "Hitachi" as vendor of device, and in the parent walk, it comes to usb-storage, which is a child of vendor/product 05e3 0735, which is listed by lsusb (Genesys Logic, Inc.,), and for which lsusb -v reports:

iManufacturer           1 USB Storage
iProduct                2 USB3.0 SATA Bridge

So, since lsusb will typically show vendor/product of, say, USB thumbdrives - why doesn't it show this drive, even if it connected through the USB bus?

Answer 1

This drive isn't a USB device, but a SATA device which is accessed via the Genesys bridge (which is a USB device). Since it isn't itself a USB device, it doesn't show up in lsusb's output.

USB thumb drives are USB devices without bridges (well, usually), so they do show up as-is on the USB bus and in lsusb's output.