Ubuntu uses at least three different icons for identifying USB storages. What are the criteria used to diferentiate those?
For instance, I have two nearly identical Sandisk Cruzer Blade USB drives, one 4 GB and other 8 GB. (The output of lsusb is the same for both: Bus 001 Device 009: ID 0781:5567 SanDisk Corp. Cruzer Blade). On Linux, one is displayed with the flash drive icon and other with the generic USB storage icon. Sometimes a third, purple icon is used too.
What is the cause of this behavior? Are there other icons? What are the rules for Ubuntu picking different USB drive icons and what do they mean?
Ubuntu differentiates between filesystem builds (ISO formats) and displays the relevant icon.
The standard USB icon is for generic removable media devices. The one with the purple usb stick is for UDF filesystems (Info here). The larger icon is for mass storage devices.
You may come across any of these depending on the hardware specifications of the device.
The icons appear based upon the partition type of the device. As of Ubuntu 21.10, older types show a rectangle with a USB symbol and newer types show a USB image with a connector at the bottom.
As of this moment, on my Ubuntu 21.10 system, they are (as listed in Disks app):