[Linux-cluster] Re: Linux-cluster Digest, Preventing LVM from concurrent access

Edson Marquezani Filho edsonmarquezani at gmail.com
Thu Aug 27 20:47:15 UTC 2009

> Yes, you can bypass the exclusive flag by hand if you dont take it into
> account when activating the exclusive LV on a second node.
> While the exclusive LV is mounted in other node, the command "lvchange
> -aey XXX/YYY" should give you an error message. "lvchange -ay XXX/YYY"
> will bypass it.

Ok, but I was able to access that LV without changing any flag, while
both nodes were joined to the cluster.

But now, I don't know why, it's working as it should be, and I can't
use the LV to launch the VM while it is running on another node, under
rgmanager control. OK. That's what I wanted.

I could move the service through servers, but sometimes it has failed.
I have done this many times in sequence, from master to slave, and
vice-versa, just waiting a few seconds between each attempt, and it
seems that sometimes the LV is not released. Anyway, such a test would
not match a real situation, so I think this can be ignored.

( I have been changing my cluster.conf a lot, so, it's difficult to
say what was wrong, if it was. Forget about. =/ )

>> I runned a test, disconecting the heartbeat link, making one server to
>> be fenced, and the VM launched on the "winner" as expected. But when
>> the "loser" server came back, still without heartbeat link, it
>> launched the same VM again, and service appeared as running locally on
>> boths nodes. I guess lvm-cluster should avoid this, shouldn't ?
> This should not happen. Have you set "exclusive=yes" into the resource
> definitions in cluster.conf? Can we have a copy of your current
> cluster.conf?

Yes, and I can say for sure that this "problem" (if I can call it like
this) keeps happening to me. Look, remember that this happens when I
bring back the server that was fenced, still without any connection
with the other, which VM was "moved" to.
 I can see that cman, clvmd, rgmanger and etc are running normaly, and
each server thinks that he is alone.

Let me try to make it easier to undestand, listing the steps I did:

1) Server A and B is up, VM service is started on cluster, and get
running on server A;
2) Cable of heartbeat interface is disconnected;
3) Server A is fenced by B, and server B starts the VM service;
4( Clabe is kept disconnected;
5) Server A is turned on again and after it has completed the
initialization, I can see that VM service is running, as well as
server B, both getting access to the same LV.

That's it, I hope you understand what I meant.

My cluster.conf with which I have runned those test is here [1].

[1] http://pastebin.com/m6a23734a

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