[issue1560] Unable to modify partition table on ThinkPad T61p during install

[Thomas Nikolajsen (via DragonFly issue tracker)]

Thomas Nikolajsen <thomas.nikolajsen at mail.dk> added the comment:

It seems like you don't have a recognized MBR on 'ad0'.
Installing an initial MBR can be done by:
  fdisk -BI ad0

Updating the MBR can be done by:
  fdisk -u ad0

If you would like to have multiple OSs installed,
a boot manager can be installed in MBR by:
  disklabel -B ad0

How did you try to modify MBR; using installer or manually?
If manually; which commands did you use?
(e.g.
  dd if=/dev/zero of=/dev/ad0 bs=512 count=32
  fdisk -BI ad0
  dd if=/dev/zero of=/dev/ad0s1 bs=512 count=32
  disklabel -w -B ad0s1 auto
  disklabel -e ad0s1
as example in disklabel man page)

Are you sure the HD you would like to modify is 'ad0'?
'da0' is first AHCI / SCSI attached disk,
'da8' is first external disk (e.g. USB attached),
'ad0' is first ATA / SATA, non-AHCI attached disk.

Your logs show several disks, ad0, ad8 & da0, in system:
  egrep '(ad|da)[[:digit:]]' DMESG
. .
ad0: 238475MB <SAMSUNG HM251JJ 2AA00 00> at ata0-master UDMA33
ad0: 488397168 sectors [484521C/16H/63S] 16 sectors/interrupt 1 depth queue
ad0: invalid primary partition table: no magic
da0 at ahci0 bus 0 target 0 lun 0
da0: <SATA HITACHI HTS72201 DCDZ> Fixed Direct Access SCSI-4 device
da0: Serial Number 071103DP1D10DGG5YHJP
da0: 150.000MB/s transfers
da0: 152627MB (312581808 512 byte sectors: 255H 63S/T 19457C)
da0: type 0x27, start 2048, end = 13860863, size 13858816 : OK
da0: type 0x7, start 13865040, end = 312575759, size 298710720 : OK
da8 at umass-sim1 bus 1 target 0 lun 0
da8: <3System USB FlashDisk 1.00> Removable Direct Access SCSI-2 device
da8: 1.000MB/s transfers
da8: 15360MB (31457280 512 byte sectors: 255H 63S/T 1958C)
da8: type 0xc, start 63, end = 31455647, size 31455585 : OK
(da8:umass-sim1:1:0:0): lost device
(da8:umass-sim1:1:0:0): removing device entry
da8 at umass-sim0 bus 0 target 0 lun 0
da8: <3System USB FlashDisk 1.00> Removable Direct Access SCSI-2 device
da8: 40.000MB/s transfers
da8: 15360MB (31457280 512 byte sectors: 255H 63S/T 1958C)
da8: type 0xc, start 63, end = 31455647, size 31455585 : OK

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<http://bugs.dragonflybsd.org/issue1560>
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