glabel clarification

[PJ]

Johan Hendriks wrote:
>> I understood that labeling a disk with glabel would permit the disk to
>> be switched to another system and booting from that disk would not
>> require other manupulations than adjusting network configuration,
>>     
> samba,
>   
>> rc.conf and a few others..
>> But what if there is already a disk on the system with the identical
>> labels in /dev/label/ ?
>> I understood that whatever the actual disk might be (ad4, ad12,
>> ad1...)would be irrelevant?
>> It would appear that the actual booting goes according to the label;
>>     
> so,
>   
>> if there are duplicate labels the boot will not necessarily be from the
>> newly installed disk if there is another disk with duplicate glabel
>>     
> labels?
>   
>> So doing a glabel seems superfluous...
>> What then is the real purpose of glabel, since the boot process seems
>>     
> to
>   
>> need a unique identifier?
>>     
>
> Switching between machines is not what labels are for.(enlighten me if
> it is)
> As far as understand, it makes switching the drive in the same machine
> easier.
> It does not matter if labels are used, that the device is seen as
> /dev/ad0 or /dev/ad{x}.
> This makes adding and replacing disk much easier.
> Sometimes the disk numbers change when removing raid controllers or
> other hardware.
>   
Yes, this is true and that is why I thought that glabel would work; I am
trying to set up my computers with identical clones that I can update
with changes on the master machine from time to time and thus prevent
data loss in case of problems. So I use ad12 as the main system; if it
were to crash I would then boot from ad6 which is identical. But the
/etc/fstab is identical in both machines. So if I boot from ad6, I will
get booted from ad12 ... so that doesn't work. It looks like we need an
unique identifier for each disk.