Thanks, I agree it looks like many people have used it OK.
I did some more digging, and while the recusrive partition error is for dev/sdj (my usb disk, another one this time), that doesnt' appear to the error. Click in 'information' for /dev/md127 gives me an error with dumpe2fs and short read on the superblock? Strange. I'm going to try parted magic, and if I get the same error, follow this guide on repairing a superblock.
http://linuxexpresso.wordpress…xt4-superblock-in-ubuntu/
Hrm.. or not.. this is from OMV..