Re: Odd behaviour after disk conversion (partition disappeared)

18.03.2022 16:52, Hartmut.Brandt@dlr.de wrote:

> Hi,
> 
> I have a virtual machine on Hyper-V running 12.1-RELEASE-p2. Root is
> mounted on /dev/da0s1a. Now we have converted the disk image from .vhdx to
> .vmdk to use it on a VMware workstation. Now the BSD partitions
> disappeared, but the thing still boots, but from /dev/ada0s1. Of course I
> cannot see the swap partition anymore.
> 
> gpart show da0 on the old image shows:
> =>      63  62914497  da0  MBR  (30G)
>         63         1       - free -  (512B)
>         64  62914495    1  freebsd  [active]  (30G)
>   62914559         1       - free -  (512B)
> 
> and gpart show da0s1:
> =>       0  62914495  da0s1  BSD  (30G)
>          0  58720256      1  freebsd-ufs  (28G)
>   58720256   3145728      2  freebsd-swap  (1.5G)
>   61865984   1048511         - free -  (512M)
> 
> on the new image gpart show ada0:
> =>      63  62914497  da0  MBR  (30G)
>         63         1       - free -  (512B)
>         64  62914495    1  freebsd  [active]  (30G)
>   62914559         1       - free -  (512B)
> 
> and gpart show ada0s1:
> gpart: No such geom: ada0s1.
> 
> What happened? The conversion process is supposed to make a 1:1 copy of
> the disk image.

I guess it was not about conversion but something else changed, too.
But the root cause is your da0s1 and da0s1a having same offset from the beginning of da0 and this is bad.

One should not create 'a' partition at zero offset inside BSD label
but either create 'b' partition at the beginning of the slice and 'a' after 'b',
or use non-zero offset for 'a'. Or else you can hit this problem with GEOM tasting order
due to ambiguity.