In addition to local disk sets, hosts can participate in named disk sets. A named disk set is any disk set that is not in the local disk set. You can implement the following types of named disk sets to manage volumes, depending on the configuration of your system.
A shared disk set can be shared by multiple hosts. Although a shared disk set is visible from all the participating hosts, only the owner of the disk set can access it. Each host can control a shared disk set, but only one host can control it at a time. Additionally, shared disk sets provide a distinct namespace within which the volume is managed.
A shared disk set supports data redundancy and data availability. If one host fails, another host can take over the failed host's disk set (this type of configuration is known as a failover configuration).
Shared disk sets are intended, in part, for use with Sun Cluster, Solstice HA (High Availability), or another supported third-party HA framework. Solaris Volume Manager by itself does not provide all the functionality necessary to implement a failover configuration.
Although each host can control the set of disks, only one host can control it at a time.
Before the autotake feature became available in the Solaris 9 4/04 release, Solaris Volume Manager did not support the automatic mounting of file systems on disk sets through the /etc/vfstab file. Solaris Volume Manager required the system administrator to manually issue a disk set take command by using the metaset -s setname -t command before the file systems on the disk set could be accessed.
With the autotake feature, you can set a disk set to be automatically accessed at boot time by using the metaset -s setname -A enable command. The autotake feature makes it possible for you to define at boot the mount options for a file system in the /etc/vfstab file. This feature allows you to define the mount options in the /etc/vfstab file for file systems on volumes in the enabled disk set.
Only single-host disk sets support the autotake feature. The autotake feature requires that the disk set is not shared with any other systems. A disk set that is shared cannot be set to use the autotake feature, and the metaset -A command will fail. However, after other hosts are removed from the disk set, it may then be set to autotake. Similarly, an autotake disk set cannot have other hosts added to it. If the autotake feature is disabled, additional hosts can then be added to the disk set.
In a Sun Cluster environment, the autotake feature is disabled. Sun Cluster handles the take and release of a disk set.
For more information on the autotake feature see the -A option of the metaset(1M) command.
Named disk sets created in a Sun Cluster environment are called multi-owner disk sets. Multi-owner disk sets allow multiple nodes to share the ownership of the disk sets and to simultaneously access the shared disks. All disks and volumes in a multi-owner disk set can be directly accessed by all the nodes in a cluster. Each multi-owner disk set contains a list of hosts that have been added to the disk set. Consequently, each multi-owner disk set within a cluster configuration can have a different (and sometimes overlapping) set of hosts.
Each multi-owner disk set has a master node. The function of the master node is to manage and update the state database replica changes. Since there is a master node per disk set, multiple masters can exist simultaneously. There are two ways that the master is chosen. The first way is that a node becomes the master if it is the first node to add a disk to the disk set. The second way is when a master node panics and fails. The node with the lowest node id becomes the master node.
Multi-owner disk set functionality is enabled only in a Sun Cluster environment to manage multi-owner disk set storage. The Solaris Volume Manager for Sun Cluster feature works with releases of Sun Cluster beginning with the Sun Cluster 10/04 software collection and with applications like Oracle Real Applications Clusters. For more information on Solaris Volume Manager for Sun Cluster, see Chapter 4, Solaris Volume Manager for Sun Cluster (Overview).
Before you can configure multi-owner disk sets, the following software must be installed in addition to the Solaris OS:
Sun Cluster initial cluster framework
Sun Cluster Support for Oracle Real Application Clusters software
Oracle Real Application Clusters software
For information on setting up Sun Cluster and Oracle Real Application Clusters software, see Sun Cluster Software Installation Guide for Solaris OS and Sun Cluster Data Service for Oracle RAC Guide for Solaris OS.