HP UX Serviceguard Storage Management Software Time Synchronization for Cluster File Systems

Cluster File System Administration

Cluster File System Administration

Any HP-UX command that can write to a raw device must be used carefully in a shared environment to prevent data from being corrupted. For shared VxVM volumes, CFS provides protection by reserving the volumes in a cluster to prevent VxFS commands, such as fsck and mkfs, from inadvertently damaging a mounted file system from another node in a cluster. However, commands such as dd execute without any reservation, and can damage a file system mounted from another node. Before running this kind of command on a file system, be sure the file system is not mounted on a cluster. You can run the mount command with no options to see if a file system is a shared or local mount.

Time Synchronization for Cluster File Systems

CFS requires that the system clocks on all nodes are synchronized using some external component such as the Network Time Protocol (NTP) daemon. If the nodes are not in sync, timestamps for creation (ctime) and modification (mtime) may not be consistent with the sequence in which operations actually happened.

Growing a Cluster File System

There is a CVM master node as well as a CFS primary node. When growing a file system, you grow the volume from the CVM master node, and then grow the file system from any CFS node. The CVM master node and the CFS primary node can be two different nodes.

To determine the primary file system in a cluster (CFS primary), enter:

#fsclustadm –v showprimary mount_point

To determine if the CFS primary is also the CVM master node, enter:

#vxdctl -c mode

To increase the size of the file system, run the following commands:

On the CVM master node, enter:

#vxassist -gshared_disk_group growto volume_name newlength

On any CFS node, enter:

#fsadm –F vxfs –bnewsize –rdevice_name mount_point

The fstab file

In the /etc/fstab file, do not specify any cluster file systems to mount-at-boot, because mounts initiated from fstab occur before cluster configuration begins. For cluster mounts, use the HP Serviceguard configuration file to determine which file systems to enable following a reboot.

Distributing the Load on a Cluster

Distributing the workload in a cluster provides performance and failover advantages. For example, if you have eight file systems and four nodes, designating two file systems per node as primary file systems will be beneficial. Primaryship is determined by which node first mounts the file system. You can also use the fsclustadm setprimary command to designate a CFS primary node. In addition, the fsclustadm setprimary

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