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Re: software raid 1: how to remove a UUID from a device?

On Fri, Dec 05, 2008 at 10:14:42AM +0100, Neil wrote:

> > Note that the physical devices /dev/sda and /dev/sdb have UUIDs
> > stored. How do I remove these UUIDs?
> >
> You can't. The UUID is calculated out of the properties of the disk
> (dunno wich exactly). It's like trying to remove the MD5 checsum of
> something: you can't.

You mean it's not stored on the disk but calculated every time? Then
how can /dev/sda have the same UUID as /dev/sdb?

As far as I understood it, mdadm writes these UUIDs so that they can
be used to recreate the arrays without entries for them in
mdadm.conf. That worked just fine on i386 when I connected the disks
after I got a larger case and installed the mdadm package. It worked
"just fine", sort of, after switching to x86_64, but differently in
that the UUIDs on the devices were "overriding" the UUIDs on the
partitions. Maybe I should send a bug report about it, but I can't
tell which version is buggy, the i386 or x86_64.

> However: your problem will be solvable and the guys who know how to do
> this are already busy.

Who is busy with this?

It's working now with the manually created entries in mdadm.conf ...

But I can't help thinking that this isn't how it should be,
i. e. maybe when installing the mdadm package, it should tell the user
what arrays have been found and will be created, and it should give
him a choice to start the md devices now or not. If I hadn't waited
for the resync on the wrongly set up array to finish, I might have
lost the data (a power failure might be enough) --- or a wrong
detection could actually destroy the data. It only asks you if and
what arrays should be brought up on system startup, and that is
obviously not enough.

"Don't let them, daddy. Don't let the stars run down."

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