boot0cfg on does not set default selection on gmirror device

[Miroslav Lachman]

Ian Smith wrote on 2016/10/21 16:43:
> On Fri, 21 Oct 2016 13:39:57 +0200, Patrick M. Hausen wrote:
>   > Hi, all,
>   >
>   > we are repeatedly bitten by the following misbehaviour of boot0cfg:
>   >
>   > root at hd45:/usr/local # boot0cfg -s 1 mirror/m0
>   > root at hd45:/usr/local # boot0cfg -v mirror/m0
>   > #   flag     start chs   type       end chs       offset         size
>   > 1   0x80      1:  0: 1   0xa5   1022:254:63        16065     16418430
>   > 2   0x00   1023:  0: 1   0xa5   1020:254:63     16434495     16418430
>   > 3   0x00   1021:  0: 1   0xa5    768:254:63     32852925   1920667140
>   >
>   > version=1.0  drive=0x80  mask=0xf  ticks=182  bell=  (0x7)
>   > options=packet,update,nosetdrv
>   > default_selection=F2 (Slice 2)
>   >
>   > So, while it should have set the default to slice 1, it simply didn't.
>
> boot0cfg isn't mirror-aware as such and thinks it's using BIOS services
> to write to a specific drive, and likely did write to one of the disks,
> but it seems gmirror isn't updating both disks' MBRs - which might not
> be too surprising.  Does it work 'sometimes'?

We are using gmirror for whole drives mirroring from the time when it 
was introduced. It was always working with MRB/BSD.

gmirror label gm0 ada0 ada1

And then you can use fdisk + bsdlabel or gpart to create slices and 
partitions and set it bootable on /dev/mirror/gm0.

I didn't tried it with FreeBSD 10.3, but it works with 8.x (we skipped 
9.x and all 8.x boxes were upgraded to 10.2 then 10.3)

Miroslav Lachman