Configuring Membership Heartbeat Regions on Disk (optional)

You can set up disk heartbeating on a shared disk to provide an additional path for VCS heartbeating (see Two Types of Channels: Network and Shared Disks). With disk heartbeating configured in addition to the private network connections, VCS has multiple heartbeat paths available. For example, if one of two private network connections fails, VCS has the remaining network connection and the disk heartbeat region that allow heartbeating to continue normally.

With disk heartbeating configured, each system in the cluster periodically writes to and reads from specific regions on a dedicated shared disk. This exchange consists of heartbeating only, and does not include communication about cluster status.

Because disk heartbeats do not support cluster communication, a failure of private network links that leaves only a disk heartbeat link between one system and the remaining nodes in the cluster causes the system to have a special jeopardy status. The system is excluded from regular cluster membership with the other systems because the status of its resources cannot be known by other systems. While the system in special jeopardy can continue to function, its resources are prevented from failing over or being switched over. This prevents possible data corruption in a split-brain situation.

The VERITAS Cluster Server User's Guide contains a description of how VCS uses heartbeating to provide cluster systems a means to determine the status of their peers and to prevent possible data corruption on shared storage. The VERITAS Cluster Server User's Guide also describes reconnecting private networks.

Editing the /etc/gabtab File to Add Heartbeat Regions

You can set up heartbeat regions on a shared disk by using gabdiskhb(1M) commands. You must enter these commands in the /etc/gabtab file identically on each system (see Configuring Group Membership and Atomic Broadcast (GAB)). The heartbeat regions on the shared disk are configured when the systems start up.

When configuring disk heartbeating, you must create two membership heartbeat regions on the disk, each consisting of 128 blocks: one for the GAB control (port a) and one for the VCS (port h).

In the following illustrated example, two systems are connected by two shared disks. Each system uses a separate controller for each disk.

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Allocation of Heartbeat Disk Regions

The illustrated configuration is specified in a /etc/gabtab file that resembles:

The -s option to the gabdiskhb command specifies the start location of each 128-block region.

The -p option specifies the port: the value "a" specifies the GAB control port, and the value "h" specifies the VCS port.

The regions should not overlap. Two adjacent regions must have starting blocks separated by 128 blocks.

Usually, the first 16 blocks of the first partition of the disk are reserved. If the partition you are using is not the first partition on the disk, the start locations may be 0 and 128.

Note the following considerations when configuring heartbeat disk regions.

• A disk partition containing a heartbeat region cannot be used for any other purpose, such as a file system or volume.
• If a disk containing heartbeat regions is also used for other purposes, the traffic could adversely affect performance of the heartbeating.

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  Note    EMC disk arrays do not support the creation of GAB disk objects, and, therefore, do not support the creation of disk heartbeat regions.

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The /etc/gabtab file is used at startup to create the regions on the disk. Reboot each system to implement the configuration. After the system starts up, you can display the configured heartbeat regions by entering:

Adding GAB Disk Region Signatures (Optional) for Integrity

To guarantee the integrity of the GAB disk region, GAB can be directed to verify a signature in that region on a periodic basis. This optional feature ensures that valuable data on the disk, such as a filesystem, is not accidently overwritten.

You can use the gabdiskconf(1M) command to initialize the region with the specified signature. This must be done before the gabdiskhb command is run manually or from the /etc/gabtab file during boot.

Example, Configuring and Checking for a Signature

In the following example, GAB disk regions are initialized by assigning signatures.

The disk regions, starting at block 16 and 144 of the block device /dev/dsk/c1t1d2s3, are assigned the 4-byte strings of 1123 and 1124, respectively, as signatures.

Later, the regions are configured as heartbeating regions by the gabdiskhb command. In the following example, the gabdiskhb command specifies that GAB check the signatures on a periodic basis.

If GAB determines that a signature does not match the user's specified value, it marks the disk as faulted.