Although it is possible to shut down the cluster on a node by invoking the shutdown procedure of the node's cluster monitor, this procedure is intended for terminating cluster components after stopping any applications on the node that have access to shared storage. VxVM supports clean node shutdown, which allows a node to leave the cluster gracefully when all access to shared volumes has ceased. The host is still operational, but cluster applications cannot be run on it.
The cluster functionality of VxVM maintains global state information for each volume. This enables VxVM to determine which volumes need to be recovered when a node crashes. When a node leaves the cluster due to a crash or by some other means that is not clean, VxVM determines which volumes may have writes that have not completed and the master node resynchronizes these volumes. It can use dirty region logging (DRL) or FastResync if these are active for any of the volumes.
Clean node shutdown must be used after, or in conjunction with, a procedure to halt all cluster applications. Depending on the characteristics of the clustered application and its shutdown procedure, a successful shutdown can require a lot of time (minutes to hours). For instance, many applications have the concept of draining, where they accept no new work, but complete any work in progress before exiting. This process can take a long time if, for example, a long-running transaction is active.
When the VxVM shutdown procedure is invoked, it checks all volumes in all shared disk groups on the node that is being shut down. The procedure then either continues with the shutdown, or fails for one of the following reasons:
Once shutdown succeeds, the node has left the cluster. It is not possible to access the shared volumes until the node joins the cluster again.
Since shutdown can be a lengthy process, other reconfiguration can take place while shutdown is in progress. Normally, the shutdown attempt is suspended until the other reconfiguration completes. However, if it is already too far advanced, the shutdown may complete first.