AIX_SN_backup_-_no_reboot

Service node takeover - no node reboot

**TBD - work in progress - not yet fully supported!**

By combining an external NFS server with a backup service node it is possible to have more highly available diskless compute nodes.

With this combination you can switch nodes to a new backup SN without rebooting the nodes.

The basic idea is that the NIM resources that are needed for the compute nodes are placed on a separate highly available NFS server instead of the service nodes. If the SN goes down the node will continue to run. As soon as the SN failure is detected you can switch to the backup SN. It will not be necessary to reboot the diskless nodes when you switch them to the backup server.

The xCAT external NFS support is currently limited to the following NIM diskless resources: SPOT, shared_root, root, paging. It does not support other NIM diskless resources, such as dump, shared_home etc. However, if the node availability is a primary concern and you do not need these other resources then you can manage the service node takeover without rebooting the nodes.

The service node switch is initiated manually using the xCAT snmove command.

A service node takeover should be initiated as soon as possible after the the current service node failure is detected.

The service node takeover with no node reboot is supported for AIX diskless nodes including stateful, stateless and statelite configurations.

Set up an external NFS server

See External_NFS_Server_Support_With_AIX_Stateless_And_Statelite for details on using external NFS server with AIX diskless nodes.

Switch to the backup service node

As described in a previous section above you can use the xCAT snmove command to switch nodes to a backup service node.

Since the node resources are mounted from the external NFS server it should not be necessary to reboot the nodes.

For example, if the SN named "SN1P" goes down you could switch all the compute nodes that use it to the backup SN by running a command similar to the following.

snmove -s SN1P