[Linux-cluster] Graceful Degradation

[gordan at bobich.net]

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?

Thanks.

Gordan

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 at axqa02rc_1 ~]# telnet axqa02rc_2 12242
> Trying 192.168.25.25...
> Connected to axqa02rc_2 (192.168.25.25).
> 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
> SHELL FENCEACKSV axqa02rc_2<singleserver>$ SHELL FENCEACKSV
> axqa02rc_2<singleserver>$ ./fence_ack_manual
> Usage:
>
> fence_ack_manual [options]
>
> 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