What storage/device type are HDD/SSD when shared with Linux on ChromeOS?

Question

On Linux, I'm used to accessing e.g. HDD data through lsblk. However, sharing my WD HDD external drive with Linux on my chromebook (appears under /mnt/chromeos/externals/) lsblk or lshw will not yield any results. Why is that? How does ChromeOS provide access to these external hard drives for the linux environment?

Background:

The 1 TB WD HDD is most likely SATA, however, when trying to analyse it through smartctl (smartmontools), I get an "inappropriate ioctl" error when specifying -d ata, and prior an "unable to detect device type" error when not manually specifying a type. I suspect this has to do with how chromeOS mounts the shared folders (from the chromeOS filesystem) to be accessible to linux.

In sum, please be so kind and help me understand the chromeOS Linux integration better. Thank you so much! :-)

Update:

findmnt yields this as only detail regarding the mounts where the "shared files" (chromeOS to linux) are mounted:

+-/mnt/chromeos                 9p
+-/mnt/external                 tmpfs

Answer 1

It looks like ChromeOS provides access to the entire /mnt/chromeos directory tree using the Plan 9 9p remote filesystem protocol.

As a result, the /mnt/chromeos/externals/ is just another remote sub-directory as far as Linux is concerned: Linux won't necessarily even know (nor care) that the external drive is a separate hardware unit. All the hardware access is managed exclusively by ChromeOS, and Linux only gets to see the files and directories using the 9p protocol. This makes it impossible to use smartctl on Linux to get SMART information from the external HDD: only ChromeOS would have the necessary hardware access to do that.