correct way to setup gmirror on 7.4?

[Ivan Voras]

On 28/04/2011 17:02, Edho P Arief wrote:
> On Thu, Apr 28, 2011 at 9:40 PM, Freddie Cash<fjwcash at gmail.com>  wrote:
>> Granted, there may be reasons why it wasn't done like this in the
>> beginning, but my non-GEOM programmer's eyes can't see any.
>
> I believe one of the reason is it would prevent conversion from
> non-gmirror disk to gmirror one as explained here
>
> http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html

Actually, storing any kind of metadata in the first sector can lead to 
weird and unexpected problems with some buggy disk controllers which 
parse the MBR for some (wrong) reasons. I personally have a disk 
controller which hangs on boot if the MBR contains anything but primary 
partitions of DOS type (even changing the partition type makes it hang), 
and that is not the only disk controller I've seen with this type of a bug.

The second reason is that storing anything except the MBR in the first 
sector makes the drive non-bootable (even if the controller is ok) and 
it is kind of nice to be able to make a cheap soft-RAID1 from two 
ordinary (S)ATA drives.