Cluster Server Installation Guide for Solaris x64 5.0 - Storage ...

Introducing VCSVCS basics15Shared storageA VCS hardware configuration typically consists of multiple nodes connected toshared storage through I/O channels. Shared storage provides multiple systemswith an access path to the same data, and enables VCS to restart applications onalternate nodes when a node fails, which ensures high availability.Figure 1-2 illustrates the flexibility of VCS shared storage configurations. VCSnodes can only access physically-attached storage.Figure 1-2Two examples of shared storage configurationsFully shared storageDistributed shared storageLLT and GABVCS uses two components, LLT and GAB, to share data over private networksamong systems. These components provide the performance and reliability thatVCS requires.■■LLT (Low Latency Transport) provides fast, kernel-to-kernelcommunications, and monitors network connections. The systemadministrator configures LLT by creating the configuration files /etc/llthosts, which lists all the nodes in the cluster, and /etc/llttab, whichdescribes the local system’s private network links to the other nodes in thecluster.GAB (Group Membership and Atomic Broadcast) provides the globalmessage order required to maintain a synchronized state among the nodes.It monitors disk communications such as the VCS heartbeat utility. Thesystem administrator configures the GAB driver by creating a configurationfile (/etc/gabtab).See “Verifying LLT and GAB configuration files” on page 129.