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Re: [Linux-cluster] Graceful Degradation

Thanks for that. Most fence methods seem to rely on external monitoring/fencing. Is there a way to get this working without external monitoring from within the initial root on a shared root system?



On Fri, 14 Dec 2007, Reiner Rottmann wrote:

Hi Gordan,

you will need to configure fencing to automatically kick out the nodes.
See [1] and [2].

As long as the cluster is not informed that the node has been kicked out
successfully, the cluster freezes the GFS volumes to prevent data corruption.

In case of a Shared Root Cluster (are you using Open-Sharedroot?) the root
filesystem is also affected because it is formatted with GFS.

If a node is successfully fenced (the nodes will get informed) , the cluster
will resume its activity. This is a protective measure.

Manual fencing which should only be used in early test environments (like [3])
require a manual fence acknowledgement. In case of Open-Sharedroot you will
need access to a special shell called fenceackshell in order to resolve a
manual fencing in progress:

[root axqa02rc_1 ~]# telnet axqa02rc_2 12242
Connected to axqa02rc_2 (
Escape character is '^]'.
Username: root
Password: somepassword
FenceacksvVersion $Revision: 1.7 $
Linux axqa02rc_2<singleserver> 2.6.9-55.0.9.ELsmp 89713 x86_64
FENCEACKSV axqa02rc_2<singleserver>$ shell
SHELL FENCEACKSV axqa02rc_2<singleserver>$ cd /sbin
axqa02rc_2<singleserver>$ ./fence_ack_manual

fence_ack_manual [options]

 -h               usage
 -O               override
 -n <nodename>    Name of node that was manually fenced
 -s <ip>          IP address of machine that was manually fenced (deprecated)
 -V               Version information

[1] http://en.wikipedia.org/wiki/I/O_Fencing
[2] http://www.redhat.com/docs/manuals/csgfs/admin-guide/ch-fence.html
[3] http://www.open-sharedroot.org/documentation/the-opensharedroot-mini-howto

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