I’m currently managing in excess of 15 completely different Slackware installs across lots of different hardware and not one of them is running a “huge” kernel, or an initrd. If a module is absolutely essential to your system’s ability to boot, why in hell haven’t you compiled it into your kernel? It’s like having a your starter-motor in your car disconnected from the battery, but having a relay on its own mini-battery connect it up when you turn the ignition.. why would you do it? What’s the point? The car will not start without it, why is it not hard wired into the system? It’s the same for the kernel. If the system won’t start without it, compile it into the kernel. Don’t play about with an injection system you don’t even need.

Ok, so your root device is inside RAID & LVM on a GPT partition. So, compile in mdadm support for your RAID level, LVM support and GPT partition support; job done.

For the less experienced, it’s also a good way to learn the basics of kernel compilation without needing to do much more than follow a standard process. All you need to do is use the config from the generic kernel you were going to boot anyway, and knowledge of what filesystem your root device is installed with and what storage controller your disk uses. Go into the kernel config, add them in [*], make, make modules_install, move and symlink the new kernel, update lilo, reboot. Once you’ve done it twice, it becomes so routine and easy you’ll wonder why you haven’t been doing it forever.

Then, once you’re more familiar with the process, you can start removing other parts of the kernel you don’t need, especially hardware controllers for hardware you don’t have, with each step making your kernel smaller and your system leaner and faster.

Have kernel, will compile.

Post followed-up by:
Compiling your own Slackware kernel