I have been running alarm from the emmc for a while now. Yesterday I took the uSD from the N900, and to my surprise arch does not boot without it. The kernel seems to load fine, but it never gets to load systemd, and I suspect rootfs never gets mounted.

If I just put in *any* uSD in the device, then arch boots fine.

I do not rule out some configuration problem in the device, but to the best of my knowledge the config is fine.

If you have arch installed to the emmc, can you try booting without a uSD and report back?