MB - breaking the mirror might let me get to the data, but might render both disks useless, so I am anxious only to go there when I have exhausted all other options (but I may have already done so).
MG23 - stupidly, I didn't take a record. I used the du -csh /* 2> ~/filelog to find the largest directory and, happy that it was not important to me, deleted it. This last time I deleted one of my own data folders - which I no longer needed - but even that was insufficient to get a proper logon.
Still stuffed ..........