Increase disk detection timeout at boot with Linux/Systemd

I've finally found it! It's of course but a simple kernel parameter, found here https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html

The parameter I was specifically looking for is rootdelay, I had already tried rootwait but apparently that wasn't enough, as it still aborted the wait after 10 seconds. Now it actually does not wait the full 30 seconds specified, but only about 10-15 seconds depending on how long it takes for my disks to show up, so setting a really high value doesn't seem to hurt, although I've only set 30 for my use case, which so far seems to have completely resolved the issue!

You can add it to your kernel boot parameters in Grub or systemd-boot.

Grub: /etc/defaults/grub -> GRUB_CMDLINE_LINUX_DEFAULT="rootdelay=30 quiet"

systemd-boot: /boot/loader/entries/yourentry.cfg -> options rootdelay=30 [other options]