Interaction Between Data Services and the Sun Cluster Software

When a data service first registers with Sun Cluster, it registers a set of call-back programs, or methods. Sun Cluster makes call-backs to the data service's methods when certain key events occur in the cluster. The remainder of this section describes the three basic methods required to make any data service run in the Sun Cluster environment. The methods are start, stop, and abort.

After the failure of a host, Sun Cluster itself moves the logical host (both its diskset and its logical network IP addresses) to one of the surviving hosts. At this point, the data service's software must be restarted on the surviving host. Sun Cluster itself cannot restart a data service. Instead, it makes a call to the data service telling it to restart itself. This call is to the data service's start or start_net method.

The Sun Cluster haswitch(1M) command smoothly shuts down a logical host on one physical server in preparation for moving the logical host to another physical server. For Sun Cluster to coordinate this shut-down work with layered data services, each data service also registers a stop method. Sun Cluster calls the data service's stop method during scadmin switch or haswitch(1M) operations, and whenever Sun Cluster is stopped using scadmin stopnode. This stop method performs a smooth, safe shutdown of the data service. This occurs without waiting for clients on the network to completely finish their work, because waiting for a client could introduce an unbounded delay.

Sun Cluster continuously monitors the health of the physical servers in the cluster. In some cases, Sun Cluster will decide that a physical server is failing, but is still able to execute some "last wishes" cleanup code before Sun Cluster halts and reboots the server. In this case, each data service is given an opportunity to execute last wishes cleanup code before Sun Cluster halts the server. Sun Cluster does this by calling the abort_net method of each data service. A data service that does not need or want the last wishes cleanup opportunity can choose not to register an abort method.