B450 Tomahawk only recognizes one bootable drive at at time

Hey y’all, wondering if anyone has an idea about this:

B450 Tomahawk (original bios, purchased May-ish 2019, legacy + UEFI boot enabled)
w/ R5 1600 @ 3.4 (+200 game boost)
16gb Adata 3000 @2933

Issue: I have three OS installed on three SATA drives - linux 5.xx /SSD; linux 4.xx /HDD, win10 /HDD… All are recognized in UEFI and boot /no issues IF each is the only drive physically connected to the board. But if two or more are connected UEFI will only recognize the last OS/drive booted - others do not show up at all. Sys seems to have no issues recognizing other/non-bootable drives - spare SATA HDDs, USB external; etc. I’ve tried swapping around SATA ports and can’t find anything in UEFI to “enable all boot options” or anything like that (searching around did turn up some results for other motherboards - apparently there is an option like that in some Asus UEFI if I remember correctly).

This isn’t really killing me since I mostly use the 5.xx; the 4.xx was only for testing some audio stuff; win10 is for [very infrequent] audio recording and currently one game I’m not really playing. But it is super annoying; hoping someone has run across this/knows how to solve in MSI UEFI or otherwise.

I dunno for sure as I don’t have a tomahawk but you might be able to at least get the two Linux working together if you have one of them use grub-install -removable to setup the grub-efi to use the fallback instead of writing it to nvram. See -

https://wiki.archlinux.org/index.php/GRUB#Installation_2
https://wiki.archlinux.org/index.php/GRUB#Default/fallback_boot_path

Hey Novastark - I appreciate the response - could prove useful in the future if I need/want an additional linux OS for some reason in the future. Unfortunately for the moment I don’t care much whether the 4.xx works - main goal is to have 5.xx/win10 available to boot w/out the extra physical step.
I forgot to mention that both the win10 and 4.xx drives/files are visible in Gnome/5.xx - only missing in UEFI menu/list - so def not a SATA/power connection issue.

Are any of your drives in the m.2 format? If I’m not mistaken, the active m.2 slots will take up SATA slots (unless NVMe? I forget) because reasons. This might be the source of your problem.

Well, now that I think about it you could just put both your Linux distros on the fallback path since they are on separate drives and have Win10 the only one in NVRAM. You’d have a proper Win10 UEFI entry and the other two could be booted into via the bios boot menu by selecting the appropriate UEFI: Drive/Port selection.

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Hey wertigon - thanks, but no m.2 in use.

Novastark - I might be unclear on exactly what you mean - but I can’t set additional drives as fallback (or active) in uefi as they aren’t recognized/visible/options… again, everything else I might have connected to the machine is shown - but the bootable drives are suspiciously missing from the list.
But maybe you mean grub or perhaps rEFind or something like that could manage the various drives?

Ditto, I thought you meant the F11? (think that is it on MSI) boot menu from the the bios and you were trying to get the other drives to show up as UEFI options there but perhaps not? If you setup grub-efi in the fallback path for those drives/distros they will appear as the drives themselves w/o a simple UEFI esp name. But you can still boot to them. It even works if you move the drives to another machine from what I understand (hence the --removable option)

TL:DR Each drive/distro has it’s own EFI bootloader that isn’t committed to NVRAM but will still show up in the boot menu. I’m using it on an MSI X470 board just fine.

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Thanks Novastark (!) - you got me looking the right direction - all OS/drives now booting from grub as fallback options under linux 5.xx.

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Cool, glad you got it sorted out. I was glad I had my setup that way when I swapped MB’s recently and didn’t have to fiddle with fixing my UEFI bootloader.

Seems silly now to have tried to do it that way in the first place. I’ve done multi-boot before but only from the same drive, and from what I saw online ppl were using UEFI to switch between OS - so I guess I assumed grub wouldn’t handle across multiple drives. And then lost the bigger picture trying to figure out why I had to unplug one bootable drive for the UEFI to recognize another - which still mystifies me a little - in that it doesn’t show a bootable drive at all, even as a non-bootable option. But whatevs; it’s much simpler this way anyhow :).