Thomas Nikolajsen <[email protected]> added the comment: Could you try booting with AHCI driver disabled (menu item at boot), and test if this makes you able to modify MBR of your <SAMSUNG HM251JJ 2AA00 00> disk (currently ad0).
If this doesn't succeed; could you try DragonFly/i386 (I see you are using DragonFly/amd64), to see if this makes any diffference being able to modify MBR. If still no success, try disabling AHCI using DragonFly/i386. _____________________________________________________ DragonFly issue tracker <[email protected]> <http://bugs.dragonflybsd.org/issue1560> _____________________________________________________
