Re: LANANA: To Pending Device Number Registrants

Heinz J. Mauelshagen
2001-05-16T17:01:45Z

On Wed, May 16, 2001 at 02:09:32PM +0200, Thomas Kotzian wrote:
> From: "Helge Hafting" <helgehaf@idb.hist.no>
> > Partition id's seems more interesting than disk id's - we normally
> > mount partitions not whole disks.
> >
> > RAID do this well - the raid autodetect partition stores an ID in the
> > last block,
> > the remaining N-1 blocks are available for a fs.
> >
> > This could be extended to non-raid use - i.e. use the "raid autodetect"
> > partition type for non-raid as well. The autodetect routine could
> > then create /dev/partitions/home, /dev/partitions/usr or
> > /dev/partitions/name_of_my_choice
> > for autodetect partitions not participating in a RAID.
>
> Raid can do this easily because they install the raid on fresh partitions so
> they can easily "steal" the last sector, and the filesystem goes in the
> "shrinked" raid-device. Normal partitions that already have a filesystem on
> them (maybe another OS formatted them) occupy space including the last
> sector - no place left on these partitions to baptize them. - how should
> that work with existing fs'es???

Right.
LVM does a similar thing storing UUIDs in its private metadata area
on every device used by it.

Problem is: neither MD nor LVM define a standard in Linux which *needs* to be
used on every device!

It is just up to the user to configure devices with them or not.

BTW: in case we had a Linux standard it wouldn't solve the
"different OS" situation mentioned in this thread either.

Generally speaking:

It is not the problem to reserve some space to store a uuid or something
at such and such location on a device.

The problem is the lack of a standard which eventually
could be implemented in all OSes at some point in time.

OS dependent data migration tools presumed, we could have
that standard in place on (all) real devices a little later than that ;-)

And what about a standard to access the stored identifying
data and to avoid that it doesn't get overwritten by accident?

>
> > This is better than volume labels, as it will work for all fs'es
> > (including those who don't support mount-by-ID) and also raw
> > partitions with no fs.
>
> Thomas Kotzian
>
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--

Regards,
Heinz -- The LVM Guy --

*** Software bugs are stupid.
Nevertheless it needs not so stupid people to solve them ***

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Heinz Mauelshagen Sistina Software Inc.
Senior Consultant/Developer Am Sonnenhang 11
56242 Marienrachdorf
Germany
Mauelshagen@Sistina.com +49 2626 141200
FAX 924446
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