glabel clarification

PJ af.gourmet at
Mon Oct 19 14:09:28 UTC 2009

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.
Here are my specifics:
I just cloned disk - ad6 from ad12...
I assume that the two are identical except for their bios assignments -
that is ad6 and ad12. Other than that they are quite identical, or 
should be.
ad12 was just glabeled, so I would assume that the clone would have all
the identical information - anyway, it looks like it does.
To test things, I booted from ad12 and then from ad6 but the boot is
always from ad12 - this is evidenced from changing the motd on ad6s1a...
the fstab on both ad4 and ad12 are identical... and dmesg shows the boot
device... so, where have I erred?

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