GPT partitioned disks have a protective mbr in the first sector of the disk, containing code to boot from the disk on non-EFI systems, along with an entry for a single slice covering the entire disk. Some BIOSes, e.g. Intel DQ965GF, will refuse to attempt to boot from a disk without an active slice. A workaround is to mark the slice as active after installing installing the pmbr, i.e. gpt boot /dev/... fdisk -a /dev/... (set slice 1 as active) It would however be preferable for gpt to do this itself, either by default, or by adding a suitable command line option.
Confirmed still a problem in 7.2-RELEASE-p2 with Intel D945GCLF2 and current BIOS. Related problems include the PMBR starting at 0xffffff -- bin/115406
State Changed From-To: open->patched This is fixed in HEAD in r198097
Responsible Changed From-To: freebsd-bugs->rnoland Over to rnoland as MFC reminder
State Changed From-To: patched->closed This is now in RELENG_7 and RELENG_8