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Subject: Re: [linux-lvm] Can't mount or run fdisk on an existing logical 
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From: "Bryn M. Reeves" <bmr@redhat.com>
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Date: Wed, 22 Jul 2009 17:49:55 +0100
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On Wed, 2009-07-22 at 17:42 +0200, Sven Eschenberg wrote:
> All 'logical' block devices behave pretty much like physical ones.
> 
> So you are free to put partition tables on top of lvs or dmcrypt block 
> devices, you can aswell put each other on top of each other. It just 
> adds possible layers of failure and or overhead.

Not really; Linux block devices don't have to support partitioning in
the kernel and this is the case for device-mapper devices.

In practice it doesn't make much difference since device-mapper also
allows arbitrary regions of existing devices to be mapped into a new
device. With a tool that can read and interpret partition table metadata
this allows partitioning to be added in user space for those devices
that don't support it natively.

> Since LVs give you the opportunity to be created in whatever size you 
> wish, in many usage cases it is perfectly normal and straight forward to 
> put a filesystem ontop of an LV instead of a partition table.

Yes, this is the typical usage. Partitioning LVs is mostly of use when
you for some reason want to treat the LV as a whole-disk image for a
device that would normally be partitioned, e.g. an image for a
virtualised system.

Regards,
Bryn.