Re: Differentiating between dm devices

[Hannes Reinecke <hare@suse.de>]

On 03/23/2011 06:30 PM, Phillip Susi wrote:
> There are different classes of dm devices that different utilities may
> or may not care about.  Some are intended to represent whole disks (
> dmraid ) that can be partitioned.  Some ARE partitions and should
> contain filesystems.  Still others are used only internally by the tools
> ( -real, -cow for lvm, and raid10 subvolumes for dmraid ).  I can not
> find any good way to differentiate between these types.
> 
And indeed you are right, there is none.

> One way of fixing this is to add a new attribute to the device where the
> tools creating them can specify a hint about what they are and how they
> should be used.  Another way is to embed that information in the UUID.
> For instance, logical volumes have UUIDs that start with "LVM-" and
> dmraid disks start with "DMRAID-".  Perhaps dmraid partitions could have
> their uuids changed to "DMRAIDP-" and internal devices changed to
> "DMRAIDI-" and "LVMI-" for dmraid and lvm respectively.
> 
That is the approach I've been following for SUSE.
The UUID is assumed to be of this syntax:

<type>-<identifier>

where <type> is defined by the program creating the mapping.
EG 'mpath' for multipath, 'partX' (where 'X' is the partition
number) for kpartx etc.

Not that these prefixes are registered in any way; would be nice
to have them registered / documented somewhere.
Cool would be to have them build into the module :-)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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