[Linux-cluster] Quorum disk over RAID software device

brem belguebli brem.belguebli at gmail.com
Tue Dec 15 20:15:30 UTC 2009

Hi Rafael,

I can already predict what is going to happen during your test

I one of your nodes looses only 1 leg of your mirrored qdisk (either
with mdadm or lvm), the qdisk will still be active from the point of
view of this particular node, so nothing will happen.

What you should consider is

1) reducing the scsi timeout of the lun which is by default around 60
seconds (see udev rules)
2) if your qdisk lun is configured to multipath, don't configure it
with queue_if_no_path or mdadm will never see if one of the legs came
to be unavail.


2009/12/15 Rafael Micó Miranda <rmicmirregs at gmail.com>:
> Hi Jacov
> El mar, 15-12-2009 a las 17:26 +0100, Jakov Sosic escribió:
>> On Tue, 2009-12-15 at 15:31 +0100, Andreas Pfaffeneder wrote:
>> > 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.
>> So you have to create mdraid on every node of the cluster? But, is that
>> legitimate way of doing things - because mdraid isn't cluster aware?
>> It's like having a LVM without using clustered volumes... It's ok as
>> long as you don't change metadata...
>> What about mdraid?
> As I see, in this situation of the usage of the shared storage volume as
> a Qdisk there is no problem of the system being "not cluster aware". I
> mean: a usual qdisk is a LUN with a "clustered" filesystem, to say it in
> some way, in which all the cluster nodes can write an read at the same
> time.
> If you don't plan to change the LVM metadata of the qdisk (I don't) I
> think this will be feasible. The same should happen with the MDADM
> variant.
> Today I configured a not-clustered volume group and then I built a
> mirrored logical volume over it and configured it as a Qdisk. Then I
> started CMAN and it worked OK using the LVM-mirror qdisk.
> Tomorrow (I hope) I'll do some tests to see what happens if only one of
> the nodes loses one of the LUNs which build the LVM-mirror volume, and
> what happens when the LUN is back.
> Thanks for your interest. Cheers,
> Rafael
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> Rafael Micó Miranda
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