Microsoft's project Silica [0] may hopefully provide really long term, large capacity archive grade storage on earth. I wonder what effects interstellar radiation has on them.
Glass is pretty inert, full stop. It would depend on the voxel size but I imagine as long as you have more than a few hundered atoms per voxel/bit you will have survivability on the order of millenia, even in high radiation environments. Someone would have to do the nuclear cross section calculations to get a real bit error rate but glass is very tough stuff.
