[ClusterLabs] DLM fencing

[Digimer]

On 08/02/16 03:55 PM, G Spot wrote:
> Hi Ken,
> 
> Am trying to create shared storage with clvm/gfs2 and when I try to
> fence I only see scsi option but my storage is conencted through FC is
> there any otherways can I fence my 1G stonith device other than scsi?

fencing of a lost node with clvmd/gfs2 is no different than normal
cluster fencing. To be clear, DLM does NOT fence, it simply waits for
the cluster to fence. So you can use IPMI, switched PDUs or whatever
else is available in your environment.

> On Mon, Feb 8, 2016 at 2:03 PM, Digimer <lists at alteeve.ca
> <mailto:lists at alteeve.ca>> wrote:
> 
>     On 08/02/16 01:56 PM, Ferenc Wágner wrote:
>     > Ken Gaillot <kgaillot at redhat.com <mailto:kgaillot at redhat.com>> writes:
>     >
>     >> On 02/07/2016 12:21 AM, G Spot wrote:
>     >>
>     >>> Thanks for your response, am using ocf:pacemaker:controld resource
>     >>> agent and stonith-enabled=false do I need to configure stonith device
>     >>> to make this work?
>     >>
>     >> Correct. DLM requires access to fencing.
>     >
>     > I've ment to explore this connection for long, but never found much
>     > useful material on the subject.  How does DLM fencing fit into the
>     > modern Pacemaker architecture?  Fencing is a confusing topic in itself
>     > already (fence_legacy, fence_pcmk, stonith, stonithd, stonith_admin),
>     > then dlm_controld can use dlm_stonith to proxy fencing requests to
>     > Pacemaker, and it becomes hopeless... :)
>     >
>     > I'd be grateful for a pointer to a good overview document, or a quick
>     > sketch if you can spare the time.  To invoke some concrete questions:
>     > When does DLM fence a node?  Is it necessary only when there's no
>     > resource manager running on the cluster?  Does it matter whether
>     > dlm_controld is run as a standalone daemon or as a controld resource?
>     > Wouldn't Pacemaker fence a failing node itself all the same?  Or is
>     > dlm_stonith for the case when only the stonithd component of Pacemaker
>     > is active somehow?
> 
>     DLM is a thing onto itself, and some tools like gfs2 and clustered-lvm
>     use it to coordinate locking across the cluster. If a node drops out,
>     the cluster informs dlm and it blocks until the lost node is confirmed
>     fenced. Then it reaps the lost locks and recovery can begin.
> 
>     If fencing fails or is not configured, DLM never unblocks and anything
>     using it is left hung (by design, better to hang than risk corruption).
> 
>     One of many reasons why fencing is critical.
> 
>     --
>     Digimer
>     Papers and Projects: https://alteeve.ca/w/
>     What if the cure for cancer is trapped in the mind of a person without
>     access to education?
> 
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-- 
Digimer
Papers and Projects: https://alteeve.ca/w/
What if the cure for cancer is trapped in the mind of a person without
access to education?