[linux-lvm] Identifying useable block devices

[Peter Rajnoha]

On 01/16/2014 10:03 PM, Paul B. Henson wrote:
>> Peter Rajnoha
>> Sent: Wednesday, January 15, 2014 9:43 PM
>>
>> This applies only if the symlinks/nodes are created directly with
>> libdevmapper - which is the old classical way.
>> If udev is used to manage /dev
>> content for dm/lvm devices then the /dev/vg/vol is a symlink to /dev/dm-X
>> (also /dev/mapper/vg-vol is a symlink to /dev/dm-X). And dm-X is not a
> 
> Hmm, yah, I see on my RHEL6 boxes that is indeed the case, as opposed to my
> older RHEL5 boxes.
> 
>> As for mount, findmnt and other utilities from util-linux - they all use
>> one common code which can handle this situation (e.g. if you call
>> "findmnt /dev/vg/vol", it shows you /dev/mapper/vg-vol on output, not
>> the dm-X the /dev/vg/vol is referencing actually).
> 
> IIRC, this thread started when somebody was being advised *not* to use the
> /dev/mapper path, but rather to use the /dev/vg path. If there is special
> case handling in util-linux, why isn't it returning what is being advertised
> as the preferable path to use rather than the one that is said to be
> internal and not to be referenced?

Well, that is probably an RFE for util-linux to give priority to
/dev/<vgname>/<lvname> instead of /dev/mapper/<vgname>-<lvname>
if it's available...

Karel, would that be possbible for you to add? (though I expect
you probably don't want to add any additional and specific logic
for dm devices :) )

-- 
Peter