HELP! GEOM: ada0: the secondary GPT header is not in the last LBA

[Warren Block]

On Fri, 19 Sep 2014, Rod Person wrote:

> Hi,
>
> I don't know what happened, but I have a 2 TB hard drive that has
> mainly multimedia on it. After a reboot I get the message:
>
> GEOM: ada0: the secondary GPT header is not in the last LBA
> GEOM_PART: integrity check failed (ada0, GPT)
>
> I found the gdisk utility and when I run I get the following
> information:
>
> root at atomizer:/ # gdisk /dev/ada0
> GPT fdisk (gdisk) version 0.8.10
>
> Partition table scan:
>  MBR: protective
>  BSD: not present
>  APM: not present
>  GPT: present
>
> Found valid GPT with protective MBR; using GPT.
>
> Warning! Secondary partition table overlaps the last partition by
> 10035073 blocks!
> Try reducing the partition table size by 40140292 entries.
> (Use the 's' item on the experts' menu.)
>
> At this point, I don't want to go any further, it would seem that I
> can restore the partition table and everything would be right again,
> but having never done this I am a bit nervous. Can anyone lend a hand
> with this?

What happened?  Was this new partition just created, and with what tool? 
gpart normally will not allow creating partitions that overlap other 
structures.  Was dd(1) used to copy it from another disk?

Is there data on this new partition?