Veritas Storage Foundation 5.0.1 Cluster File System Administrator's Guide Extracts for the HP Serviceguard Storage Management Suite on HP-UX 11i v3

I/O Error Handling Policy
I/O errors can occur for several reasons, including failures of FibreChannel links, host-bus
adapters, and disks. CFS disables the file system on the node that is encountering I/O errors, but
the file system remains available from other nodes. After the I/O error is fixed, the file system
can be forcibly unmounted and the mount resource can be brought online from the disabled
node to reinstate the file system.
About Veritas Cluster Volume Manager Functionality
With CVM, a set of VxVM disks can be accessed simultaneously by multiple, or all, cluster nodes.
The same logical view of the disk configuration and any changes are available on each node.
When the cluster functionality is enabled, all cluster nodes can share VxVM objects. Features
provided by the base volume manager, such as mirroring, fast mirror resync, and dirty region
logging are also supported in the cluster environment.
NOTE: RAID-5 volumes are not supported on a shared disk group.
To implement cluster functionality, VxVM works together with the cmvx daemon provided by
HP. The cmdx daemon informs VxVM of changes in cluster membership. Each node starts up
independently and has its own copies of HP-UX, Serviceguard, and CVM. When a node joins a
cluster it gains access to shared disks. When a node leaves a cluster, it no longer has access to
shared disks. A node joins a cluster when Serviceguard is started on that node.
Figure 2-1 illustrates a simple cluster consisting of four nodes with similar or identical hardware
characteristics (CPUs, RAM and host adapters), and configured with identical software (including
the operating system). The nodes are fully connected by a private network and they are also
separately connected to shared external storage (either disk arrays or JBODs) via Fibre Channel.
Each node has two independent paths to these disks, which are configured in one or more
cluster-shareable disk groups.
The private network allows the nodes to share information about system resources and about
each other’s state. Using the private network, any node can recognize which nodes are currently
active, which are joining or leaving the cluster, and which have failed. The private network
requires at least two communication channels to provide redundancy against one of the channels
failing. If only one channel is used, its failure will be indistinguishable from node failure—a
condition known as network partitioning.
Figure 2-1 Example of a Four-Node Cluster
Redundant
Fibre Channel
Connectivity
Cluster-Shareable
Disks
Redundant Private Network
Node 0
Master
Node 1
Slave
Node 2
Slave
Node 3
Slave
Cluster-Shareable
Disk Groups
About Veritas Cluster Volume Manager Functionality 19