Well, I've ordered a power supply and lets see what happens there first. Its a 380W unit so should be able to handle the loads. It seems interesting that the rebuild is okay..which is heavily hitting both disks...but large writes and reads (especially reads) fail and break gmirror.
This will be okay until I decide to replace the MB...I'll probably need to upgrade the PSU again.
this was supposed to be a cheap project.....