[Ocfs2-users] mounting mpath devices

[Joel Becker]

On Tue, Feb 24, 2009 at 02:21:03PM -0700, Masaryk Kevin D wrote:
> I'm seeing some strange behavior from OCFS2 while trying to mount
> mpath/dm-multipath devices under RHEL5. Sometimes I can mount the
> EMC-connected, dual-pathed volumes just fine and sometimes I get "device
> busy" errors. I've tried mounting by label and also by explicit
> /dev/mapper/mpathXpY name with the same unpredictable behavior. I've
> also noticed that sometimes when a device is successfully mounted on all
> nodes, each node may return different output from the mount command
> regarding the device mounted; e.g. /dev/mapper/mpath0p1 vs. /dev/dm-17.

	I'm unsure as to why you get the 'device busy' errors.  That's
the weird thing.  Mounting by label makes you vulnerable to the whims of
blkid - whichever /dev name it finds first is what you'll see in the
output of mount(8).  But in the end, it should be the same device (that
is, /dev/mapper/mpath0p1 is probably the same thing as /dev/dm-17).

> One consistent aspect I have noticed whenever I receive the "device
> busy" error is that the /dev/dm-X names don't match up on each node. I
> also see that ocfs2console refers to each device by the /dev/dm-X name
> instead of the /dev/mapper/XX name.

	The /dev/dm-X names are not intended to match up.  They appear
in the order the system discovers them.  The multipath daemon is
responsible for matching the /dev/dm-X name to the consistent
/dev/mapper/mpathXpY name.  So if you want to see a consistent name, use
that one.

> I guess my question is simply: Are dm-multipath devices supported under
> OCFS2? Are multipathed devices not recommended with OCFS2? Any
> documentation available on this?

	They should work, and they are absolutely recommended.

Joel
-- 

"If at first you don't succeed, cover all traces that you tried."
                                                        -Unknown

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127