[Linux-cluster] Multipathed quorum disk

[Alain RICHARD]

Le 1 sept. 07 à 02:57, Claudio Tassini a écrit :

> Hi,
>
> I recently upgraded a 2-nodes cluster adding two more nodes. I  
> would like a single node to remain in cluster even if the other  
> three are out of service, so I'm trying to add a quorum disk to the  
> cluster.
>
> The problem is that the quorum disk is a LUN in a shared storage  
> which has not the same device name through all the cluster nodes.  
> Moreover, we use device-mapper AND lvm. I could resolve the problem  
> using an lvm logical volume, because it would always have the same  
> name and recognize the underlying "dm" or "sd" device name even if  
> it changes across a reboot, but I've read that it's not advisable  
> to use a logical volume as quorum device.
>
> Any idea?
>
> -- 
> Claudio Tassini
> --
> Linux-cluster mailing list
> Linux-cluster at redhat.com
> https://www.redhat.com/mailman/listinfo/linux-cluster


using multipath -ll you'll see that your multipath device has got a  
unique id (wwid) :

# multipath -ll
/dev/mpath/mpath2 (200c0b60a76000032) dm-3 SNAP,FILEDISK
[size=10M][features=0][hwhandler=0]
\_ round-robin 0 [prio=0][active]
\_ 2:0:0:0 sdd 8:48  [active][ready]
\_ 1:0:0:0 sdc 8:32  [active][ready]

all you have to do then, is to modify your /etc/multipath.conf file  
to ask a fixed name for this multipath device instead of having it  
get a dynamique name (/dev/mpath/mpathx) :

/etc/multipath.conf :

...
multipaths {
         multipath {
                 wwid                    200c0b60a76000032
                 alias                   qdsk1
         }
}

and then :

# multipath -ll
[root at titan2 ~]# multipath -ll
qdsk1 (200c0b60a76000032) dm-4 SNAP,FILEDISK
[size=10M][features=0][hwhandler=0]
\_ round-robin 0 [prio=0][active]
\_ 4:0:0:0 sdf 8:80  [active][ready]
\_ 3:0:0:0 sde 8:64  [active][ready]

(please, be warn that the first time you do it, it rename the  
multipath device to the name you have ask for, but it fails to rename  
the /dev/mpath/ device, so you have to do it manually once).

do it on all your cluster members and they all get the multipath  
device with the same name.

I have also encoutered a problem with cman that refuse to register a  
node with more than 16 chars (qdiskd register the qdisk device as a  
node name). So you must ensure your device path is less than 16 chars  
for a qdisk device (this is why I use /dev/mpath/qdsk1 instead of / 
dev/mpath/qdisk1).

Regards,

-- 
Alain RICHARD <mailto:alain.richard at equation.fr>
EQUATION SA <http://www.equation.fr/>
Tel : +33 477 79 48 00     Fax : +33 477 79 48 01
E-Liance, Opérateur des entreprises et collectivités,
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