I thought the issue was that you couldn't write to it?IIRC, you can read and write to it but you can't boot from it. Support for booting from the HD20 was removed from the SE/30's ROM.
Some people are still having problems connecting their HD20 to their SE/30, like James Wages. Some hack is required to boot from it I think.
I've heard of this, but never seen it. Do you have a link where it can be found?Look up the MacIIHD20 INIT.