gconcat question

[John Nielsen]

On Sunday 19 October 2008, Roger Olofsson wrote:
> <-----Ursprungligt Meddelande----->
>
> >From: John Nielsen [lists at jnielsen.net]
> >Sent: 19/10/2008 3:39:00 AM
> >To: freebsd-questions at freebsd.org
> >Cc: raggen at passagen.se
> >Subject: Re: gconcat question
> >
> >On Saturday 18 October 2008, Roger Olofsson wrote:
> >> What are the steps to bring back gconcatenated disks if doing an
> >> upgrade from FreeBSD6 to FreeBSD7 like this?
> >>
> >> As-is situation:
> >> FreeBSD 6.2-STABLE ad0 has FreeBSD ad1, ad2 and ad3 are gconcatenated
> >> using 'gconcat label -v data /dev/ad1 /dev/ad2 /dev/ad3'.
> >
> >The concat device should just appear automatically after the upgrade as
> >long as you (continue to) load the geom_concat kernel module. Be aware
> >that if
> >the on-disk metadata format has changed then it will automatically be
> >upgraded. This is usually a good thing but if you need to roll back to
> >6.x for some reason it's something to take into consideration.
> >
> >> Planned upgrade:
> >> Reboot from cdrom, install FreeBSD7 from cd to ad0
> >
> >Just curious, is there a reason you're going this route instead of
> >upgrading from source?
>
> Hello John and thank you for your reply!
>
> Follow-up question - /dev contains a /dev/concat/label entry - is this
> entry created when loader.conf invokes the kernel module?

Yes. Many of the GEOM modules (label, mirror, concat, stripe, etc) create 
nodes in the relevant subdirectories in /dev as soon as they "taste" the 
drives (or other providers) and discover metadata belonging to them. This 
is generally when they are loaded (if modules) or at boot time (if compiled 
into the kernel or preloaded by loader.conf). Any time you insert a device 
(such as a USB stick) the loaded modules also have an opportunity 
to "taste" it and create nodes as appropriate.

> The machine won't be rollbacked so that's not an issue.
>
> The reason for following this route is that it's faster than doing it
> from source (it's an old machine). The machine has been a playground and
> has alot of ports installed that aren't being used anymore. The
> concatenated drives contain data only hence the need to preserve those.

Makes sense. :)

JN