CFS Overview

A file system cluster consists of one primary, and up to fifteen secondaries. The primary-secondary terminology applies to one file system, not to a specific node (or hardware platform). So it is possible to have the same cluster node be primary for one shared file system, while at the same time it is secondary for another shared file system. Such distribution of file system primaryship to balance the load on a cluster is a recommended administrative policy (Distributing the Load on a Cluster).

For CVM, a single cluster node is the master for all shared disk groups and shared volumes in the cluster.

Cluster/Shared Mounts

A VxFS file system that is mounted with the mount –o cluster option is called a cluster or shared mount, as opposed to a non-shared or local mount. A file system mounted in shared mode must be on a VxVM shared volume in a cluster environment. A local mount cannot be remounted in shared mode and a shared mount cannot be remounted in local mode. File systems in a cluster can be mounted with different read-write options. These are called asymmetric mounts.

CFS Primary and CFS Secondary

The primary file system handles the metadata intent logging for the cluster file system. The first node of a cluster file system to mount is called the primary node. Other nodes are called secondary nodes. If a primary node fails, an internal election process determines which of the secondaries becomes the primary file system.

Use the following command to determine primaryship:

Use the following command to give primaryship to a node:

A cluster file system node can be mounted using the mount seconly option to prevent it from ever assuming the primaryship of the cluster. If a primary node fails and all the remaining nodes in the cluster file system are mounted as secondary-only, the cluster is disabled. The mount seconly option overrides any setting by the fsclustadm command. See the mount_vxfs(1M) man page for more information on the seconly option.

Asymmetric Mounts

Asymmetric mounts allow shared file systems to be mounted with different read/write capabilities. So one node in the cluster can mount read-write, while other nodes mount read-only.

You can specify the cluster read-write (crw) option when you first mount the file system, or the options can be altered when doing a remount (mount –o remount). The first column in the following table shows the mode in which the primary is mounted. The check marks indicate the mode secondary mounts can use.

Only mounting the primary with –o cluster,ro prevents the secondaries from mounting in a different mode, that is, read-write mode. Note that rw implies read-write capability throughout the cluster.

See the mount_vxfs(1M) man page for information on the cluster read-write (crw) mount option.

CFS and CVM Agents

Agents are VCS processes that manage predefined resource types. CFS and CVM require agents to interact with VCS. Agents bring resources online, take resources offline, monitor resources, and report any state changes to VCS. VCS bundled agents are part of VCS and are installed when VCS is installed. The CFS and CVM agents are add-on resources to VCS specifically for the VERITAS File System and VERITAS Volume Manager (see Agents for SFCFS/SFCFS HA for detailed information on CFS and CVM agents).