How to predict drive number change for 7.3->8.1 upgrade?

Michael Sperber sperber at
Thu Sep 16 09:56:58 UTC 2010

Stefan Bethke <stb at> writes:

> Am 16.09.2010 um 11:05 schrieb Michael Sperber:
>> I just upgraded my desktop system from 7.3 to 8.1, and the main hard
>> drive, which was /dev/ad6 before is now /dev/ad10.  Consequently, the
>> initial boot failed when trying to mount the root file system from ad6.
>> The desktop system is now fixed, but I also have a rented server with
>> only a serial console, and I worry that the upgrade is going to leave me
>> with a dead machine.  Is there any way to predict how the drive number
>> changes?  (Why does it change at all?)  If so, what's the proper way to
>> tell the system the initial root device *before* rebooting?
> If you have a serial console, you can always enter the root device at
> the prompt, so you can recover there.

I know.  But given the serial-console problems recently reported here, I
was a bit reluctant to take the risk.

> Long-term, the best option is to label your filesystems or partitions,
> and use the label entries in fstab instead of the device names.  I
> don't remember what 7.3 offers in terms of labels, but glabel should
> be available.  Check tunefs if it offers the -L volname option, that's
> even better.

That sounds like a good idea.  Thanks!


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