Comment 7 for bug 118956

From man dmraid:

 {-r|--raid_devices} [device-path...]
              List all discovered RAID devices with format, RAID level, sec‐
              tors used and data offset into the device. In case a metadata
              format handler is chosen with -f , only RAID devices with such
              format can be discovered. Useful if devices have multiple meta‐
              data signatures....
              If -E is added to -r the RAID metadata on the devices gets con‐
              ditionally erased. Useful to erase old metadata after new one
              of different type has been stored on a device in order to avoid
              discovering both.

Infact:

cesare@desktop:~$ sudo dmraid -E -f nvidia /dev/sda
Password:
ERROR: option missing/invalid option combination with -f

In any case, thanks for the tip; I deleted the wrong metadata adding the -r.
Still doesn't get automounted and I'm really puzzled how and what wrote that metadata. Any idea?