The original firmware wasn't loading at all - the hard disks were crashed and someone (as far as I know) did a firmware upgrade which didn't go well.
I followed this https://wiki.ccc-ffm.de/projekte:diverses:seagate_blackarmor_nas_220_debian
to compile / reflash an up-to-date u-boot.
I guess I could go with debian, but lede/openwrt is much faster/smaller