On 2012-04-04T11:28:31, Rainer Krienke <[email protected]> wrote:
> There is one basic thing however I do not understand: My setup involves
> only a clustered filesystem. What I do not understand is why a stonith
> resource is needed at all in this case which after all causes freezes
> of the cl-filesystem depending on the timeout values.
>
> Basically in a cluster fs it should be not important if a node dies. Its
> the nature of a cluster fs that many nodes can acces it. If one dies
> this is of no meaning to the other nodes that still can access the
> filesystem.
You're getting that exactly the wrong way around ;-)
In a cluster file system, concurrent access from multiple nodes is
expected. Hence, the file system needs to coordinate writes (but also
some reads), metadata updates, assigning new blocks, etc across the
nodes to remain consistent.
If the two nodes can no longer communicate, they could potentially write
to the same block. Hence, if they can no longer communicate (network
failure or node down), the cluster needs to reach a consistent state
first, recover the file system portion accessed by the removed node,
etc.
> So my question comes down to this: Why do I have to fence a node (in
> case it failes) in a cluster that has nothing else but a cluster
> filesystem. What could go wrong without fencing in this case?
As long as you have reasonably uptodate backups to recover from the data
corruption that will ensue, not all that much ;-)
A non-clustered fs would continue to operate (so no freeze), but you'd
still see a fence to make sure the node is truly down before a fail-over
was done.
Regards,
Lars
--
Architect Storage/HA
SUSE LINUX Products GmbH, GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer, HRB
21284 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde
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