Bug 234471

Summary: multipath devices (dm-?) will not be created in /dev/
Product: [Fedora] Fedora Reporter: Arne <arne.brieseneck>
Component: device-mapper-multipathAssignee: Ben Marzinski <bmarzins>
Status: CLOSED NOTABUG QA Contact: Corey Marthaler <cmarthal>
Severity: medium Docs Contact:
Priority: medium    
Version: 6CC: agk, bmarzins, christophe.varoqui, dwysocha, egoggin, junichi.nomura, kueda, lmb, mbroz, prockai, tranlan
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Target Release: ---   
Hardware: x86_64   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
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Clone Of: Environment:
Last Closed: 2007-03-30 23:40:21 UTC Type: ---
Regression: --- Mount Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Arne 2007-03-29 15:03:09 UTC
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Description of problem:
Hardware: SUN X4100 2AMD 285 16GB ISCSI over Silverback iSNAP HBA 2path
 
when I boot, the multipath is working fine and the devices are created well under /dev/mapper/mpath[0-n] and I can see underlying devices in cat /proc/partitions
 
I do see as well the within that list (proc/partitions) that there are multipath-devices dm-0, dm-1, dm2 .... but this devices are not created under /dev/
 
 
So, I can create the nodes with mknod dm-0 b 253 0 and so on, and mount the multipathed device then, but this is not boot safe. After a boot this manually created devicenodes are gone and I have to do it by myself again. Really strange is, that this "dm-n" devices are there and named as you can see in multipath -ll or in cat /proc/partitions but the nodes are never created. 

Version-Release number of selected component (if applicable):


How reproducible:
Always


Steps to Reproduce:
1. boot
2. cat /proc/partitions | grep dm-
3. ls -la /dev/dm*

Actual Results:
after 2.) I see dm-0, dm-1 and dm-2 created
after 3.) I get a no such file or directory

Expected Results:
after 2.) OK
after 3.) I would expect a devicenode

Additional info:

Comment 1 Ben Marzinski 2007-03-30 23:40:21 UTC
In fc6, the udev rules for device-mapper devices don't create /dev/dm-* devices.
This is actually a good thing. There is no guarantee that these device names will
always point to the same device. For instance if on one boot /dev/dm-1 points to
your LVM root volume, on another boot, it could be that /dev/dm-2 points to it.
So referencing devices by these names is not safe.  Further, the /dev/dm-* names
are not created until udev runs, so if you need to access a device early in the
boot process, you must use the /dev/mapper name. Really, there is no good reason
to ever use the /dev/dm-* names. You should always use the /dev/mapper ones. It
is unfortunate that /proc/partitions references them by the /dev/dm-* name.