How to list an UUID?

[Daniel Pittman]

Felipe Figueiredo <philsf at ufrj.br> writes:
> On Thursday 29 March 2007 03:11:22 Daniel Pittman wrote:
>
>> Perhaps you had some other question in mind though?
>
> Maybe something like: "can one use UUIDs from LVM volumes?", or "if I
> resize the LVM volume, will its UUID change?"
>
> I only know the answer to the first one, and it's a yes.

I don't quite follow these questions either, but I do understand why I
don't follow them:

You seem to be conflating two different "layers" into one: LVM and the
UUID stuff.

LVM is a block device management layer.  It just exports space from
whatever source as a single block device with certain properties.

The UUID that is used to mount is a *filesystem* property: ext3, XFS,
Linux swap, etc all have their own UUID somewhere in their headers.

So -- an LVM logical volume doesn't have a UUID that is used in the
mount process at all.

A file system -- on LVM, on an MD software RAID, on hardware RAID or
whatever -- has a UUID.


So: if you resize your LVM volume the UUID stays the same.

If you reformat your LVM volume with a new file system, no changes at
the LVM level, your UUID changes.


In other words: LVM isn't relevant to the UUID used for mounting or
whatever.


Oh, and finally: LVM scans all available hardware (by default) to find
the PVs that it uses.  It doesn't depend on the UUID or whatever because
it implements a scheme all of its own to handle relocated hardware.

Regards,
        Daniel
-- 
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