Bootable usb key not showing up.

Dear Community,

Tricky case here that will please the experts and will challenge them.

I bought 2 usb keys that are known to be really fast. 1 is Kingston Data Traveler Max, 256 GB, with write and read speed of respectively 1000/900 Mbs. The other one is Transcend ESD310C 256 GB with similar performance. This last one is a duo (both USB A and USB C) while the first one is only USB A (USB C exists and I have one as well).

The DT Max is sold as a USB pendrive or key, while the ESD310C is sold as an SSD. But I think that both have the same technology. Whatever it means, mac Os sees them as non-removable SSDs and not as removable usb keys.

I can format, partition and create as many bootable volumes as I want with both keys, exactly as I did with a "real" usb key (Sandisk Ultra Dual Drive Pro) and this is working fine, in a nutshell.

Problem is: once this is done and I try to boot on any of these volumes, they are just not showing up. While those on the Sandisk appear as expected.

I also noticed with the DT Max some latences while I was using createinstallmedia command in Terminal that I never face with a standard usb key or even an external SSD (did the test as well with Sandisk Extreme Pro).

It looks like mac Os does not figure out whether it is facing a usb "protocol" or an SSD "protocol" (dunno which term to use here) and result is that I cannot boot on any of those two devices. While I perfectly see and manipulate the content in either Terminal or Disk Utility. I have to admit that this is driving me crazy.

Anyone facing the same kind of issues with similar devices? More important, anyone with at least an explanation and/or, even better, a fix?

Thanks a bunch for your help, buddies.

Quick update here: I wrote an email to Kingston support explaining the issue. Will try to do the same to Transcend.

Regarding Kingston, other consumers reported same issue with external SSD XS2000 model.

Will update this post upon answer reception if ever.

Received answer from Transcend: « Apple’s fault ». Great…

Now while driving to the office this morning, was just thinking that the Mac was not able to mount the EFI partition from the usb at startup. Cannot be any other root cause I guess. Question is: why?

I know this little utility called mountEFi on Mac Os, will try to check what’s inside after the bootable creation process. And will check as well if my Ventoy key is visible at least on the boot menu on Mac, as I created it using exFat for the standard partition and considering the VTOYEFI partition is Fat32.

By the way I will check which format the EFI partition created on Mac by the createinstallmedia command is

Just read Wiki page for EFI definition and use, specifically for Mac Os. My assumption here above may not be correct as it is said that bootloader is not stored in the EFI partition… 😕