Números y medida de magnitudes. Segmentos inconmensurables

Packages have somewhat different behavior in a continental cluster than in a normal ServiceGuard environment. There are specific differences in

• Startup and Switching Characteristics

• Network Attributes

Startup and Switching Characteristics

Normally, an application (package) can run on only one node at a time in a cluster. However, in a continental cluster, there are two clusters in which an application—the primary package or the recovery

package—could operate on the same data. The primary package and the recovery package must not both be allowed to run at the same time. To prevent this, it is very important to ensure that packages are not allowed to start automatically and are not started up at inappropriate times.

To keep packages from starting up automatically when a cluster starts, you must set the AUTO_RUN (PKG_SWITCHING_ENABLED used prior to ServiceGuard 11.12) parameter for all primary and recovery packages to NO. Then use the cmmodpkg command with -e <packagename> option to start up only the primary packages and enable switching. The cmrecovercl command, when run, will start up the recovery packages and enable switching during the cluster recovery operation.

WARNING After initial testing is complete, the cmrunpkg and cmmodpkg commands or the equivalent options in SAM should never be used to start a recovery package unless cluster recovery has already taken place.

To prevent packages from being started at the wrong time and in the wrong place, you can use the following strategies:

• Set the AUTO_RUN(PKG_SWITCHING_ENABLED used prior to ServiceGuard 11.12) parameter for all primary and recovery packages to NO.

• Ensure that recovery package names are well known, and that personnel understand they should never be started with a cmrunpkg or cmmodpkg command unless the cmrecovercl command has been invoked first.

Building a Continental Cluster

Understanding Continental Cluster Concepts

• Once the continental cluster is in production, create special scripts for the execution of the ServiceGuard commands cmrunpkg and

cmmodpkg. A script could be written that would run the cmrunpkg or cmmodpkg command, but exit with an error or warning message if someone inadvertently tried to start a specified list of your recovery packages with these commands.

• If a cluster has no packages to run before recovery, then do not allow packages to be run on that cluster with SAM.

Network Attributes

Another important difference between the packages in a continental cluster and the packages configured in a standard ServiceGuard cluster is that different subnets are used in recovery packages than the subnets in the primary packages. The client application must be designed to reconnect to the appropriate IP address following a recovery operation.

How MC/ServiceGuard commands work in a ContinentalCluster

ContinentalClusters packages are manipulated manually by the user via ServiceGuard commands and by cmcld automatically in the same way as any other packages.

In a continental cluster the recovery package are not allowed to run at the same time as the primary, data sender, or data receiver packages. To enforce this, several MC/ServiceGuard commands behave in a slightly different manner when used in a continental cluster.

Table 5-2 describes the ServiceGuard commands whose behavior is different in a continental cluster environment. Specifically, when one of the following commands attempts to start or enable switching of a package, it first checks the status of the other packages in the recovery group. Based on this status, the operation is either allowed or disallowed.

Understanding Continental Cluster Concepts

Table 5-2 ServiceGuard and ContinentalClusters Commands

Commands How the commands work in SG

How the commands work in ContinentalClusters

cmrunpkg runs a package will not start a recovery package if any of the primary, data receiver, or data sender package is in the same recovery group is running or enabled. will not start a primary, data receiver, or data sender package if the recovery package in the same recovery group is running or enabled.

cmmodpkg -e enable switching attribute for a highly available package

will not enable switching on a recovery package if any of the primary, data receiver, or data sender package is in the same recovery group is running or enabled. will not start a primary, data receiver, or data sender package if the recovery package in the same recovery group is running or enabled.

Building a Continental Cluster

Understanding Continental Cluster Concepts

cmhaltnode -f halts a node in a highly available cluster

will not re-enable switching on a recovery package if any of the primary, data receiver, or data sender package is in the same recovery group is running or enabled. will not start a primary, data receiver, or data sender package if the recovery package in the on a recovery package if any of the primary, data receiver, or data sender package is in the same recovery group is running or enabled. will not start a primary, data receiver, or data sender package if the recovery package in the same recovery group is running or enabled Table 5-2 ServiceGuard and ContinentalClusters Commands

Commands How the commands work in SG

How the commands work in ContinentalClusters

Designing a Disaster Tolerant Architecture for use with ContinentalClusters

Designing a Disaster Tolerant Architecture