If you use an initrd (which you probably do if you're using the generic kernel as recommended), you can also add dmraid -ay to your "init" file in /boot/initrd-tree. You have to include the dmraid files to /boot/initrd-tree and rebuild initrd, but that is actually very straightforward.
The advantage is that you can then not only mount your fakeraid, you can actually boot off of it or use it as swap, or encrypt it with LUKS or all the above. There's a pretty good howto thread here somewhere outlining the process.
Here it is:
https://www.linuxquestions.org/quest...k-12.0-586440/
You can find others with search "dmraid Slackware"