[Linux-cluster] Quorum disk over RAID software device

[Rafael Micó Miranda]

Hi Andreas

El mar, 15-12-2009 a las 15:31 +0100, Andreas Pfaffeneder escribió:
> Hi Rafael,
> 
> Am 14.12.2009 23:15, schrieb Rafael Micó Miranda:
> > Hi all,
> >
> > I was wondering if there is a way to achieve a "quorum disk over a RAID
> > software device" working CMAN cluster.
> >
> >    
> in a similar situation I am using a raid-1 device (built with mdadm 
> prior to the startup of cman/rgmanager) which consists of two luns, one 
> in each location. This works pretty well as quorum-device.
> 
> Andreas
> 
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Today I tried this approach, but I have no previous experience with
MDADM. The problem I found was, how do you manage multipath on the
different LUNs without device-mapper-multipath?

As I see in the system logs the MD driver loads before
device-mapper-multipath is working, and it uses the devices (/dev/sdX)
to assemble the RAID devices (/dev/mdX) before the devices are available
through device-mapper-multipath (/dev/mapper/quorumdiskX) at system boot
time. This even makes the device-mapper-multipath devices not getting
built when multipathd starts after that. Does this happen to you? 

So, I tried to configure a multipath device with MDADM and after that
use the built devices to assemble a RAID1 MD device. This was the config
in mdadm.conf I used:

DEVICE /dev/sd*

ARRAY /dev/md1 metadata=1.1 level=multipath num-devices=2
name=multipath01 
ARRAY /dev/md2 metadata=1.1 level=multipath num-devices=2
name=multipath02
ARRAY /dev/md3 metadata=1.2 level=raid1 num-devices=2 name=quorum
devices=/dev/md1,/dev/md2

Devices where all with the "Linux raid auto" partition mark. When I
built the MDs first everything seemed to work, but after a system boot
the /dev/md3 device was not built, so the quorum disk would not be
available for CMAN.

How do you implement this with MDADM?

Thanks in advance,

Rafael

-- 
Rafael Micó Miranda