10    Using Logical Storage Manager in a Cluster

Using LSM in a cluster is like using LSM on a single system. The same LSM software subsets are used for both clusters and standalone configurations.

For complete documentation on LSM, see the Tru64 UNIX Logical Storage Manager manual. Information on installing LSM software can be found in that manual and in the Tru64 UNIX Installation Guide.

In a cluster, LSM provides the following features:

• High availability

  LSM operations continue despite the loss of cluster members, as long as the cluster itself continues operation and a physical path to the storage is available.

• Performance:

  • For I/O within the cluster environment, LSM volumes incur no additional LSM I/O overhead.

    LSM follows a fully symmetric, shared I/O model, where all members share a common LSM configuration and each member has private dirty-region logging.

  • Disk groups can be used simultaneously by all cluster members.

  • There is one shared rootdg disk group.

  • Any member can handle all LSM I/O directly, and does not have to pass it to another cluster member for handling.

• Ease of management

  The LSM configuration can be managed from any member.

10.1    Differences Between Managing LSM in Clusters and in Standalone Systems

The following restrictions apply to LSM in a cluster:

• LSM volumes cannot be used for the boot partitions of individual members.

• LSM cannot be used to mirror a quorum disk or any partitions on that disk.

• LSM Redundant Array of Independent Disks (RAID) 5 volumes are not supported in clusters.

• To place the cluster_root, cluster_usr, or cluster_var domains under LSM control, you must use the volmigrate command.

The following LSM behavior in a cluster varies from the single-system image model:

• Statistics that are returned by the volstat command apply only to the member on which the command executes.

• The voldisk list command can give different results on different members for disks that are not part of LSM (that is, autoconfig disks).

  The differences are typically limited to disabled disk groups. For example, one member might show a disabled disk group and on another member that same disk group might not show at all. In addition, in a cluster the voldisk list command displays only those non-LSM disks that are directly connected to the member on which the command was executed.