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Re: [Cluster-devel] use cman_tool leave remove on shutdown/restart



On 09/26/2011 12:55 PM, Dietmar Maurer wrote:
>> The leave "remove" option has to be used only when permanently removing a
>> node from a cluster.
>> The "remove" code path, totally cancel the knowledge of that node from the
>> cluster, including quorum recalculation.
>>
>> It has to be used very carefully for example when doing some long planned
>> maintenance of the node.
> 
> Well, I thought a 'shutdown' indicates that the node will be down for some time?

"some time" is a relative concept.. and there is no perfect boundary.

Let me explain.

Doing a "leave remove" involves other operations on the remaining nodes
to update cluster.conf (for example) to drop that node that's gone.

If your "shutdown" is maybe 10 minutes or 60 minutes to replace one PSU
(or whatever) it might not be worth at all to remove the node from the
cluster in full.

Other users might deem necessary to reconfigure the cluster for that.

Remember you also have a very strict process to readd a node to the cluster.

So it is up to the sysadmin to decide if a 10 minutes or XX hours
downtime is dangerous enough to require a cluster config vs "cluster can
easily operate without a node".

It also strictly depends on the size of the cluster.

There is a corner case (far away) where you could have 2 quorate cluster
forming again (after a leave remove) and that would be BAD.

So leave remove is one option that cannot be enabled by default (it is
indeed dangerous, even for some small corner cases, they can still
happen) but it is there as a tool for cluster admins when necessary (and
has to be used carefully and knowing what is happening internally).

Fabio


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