VERITAS Storage Foundation 4.1 Cluster File System HP Serviceguard Storage Management Suite Extracts, December 2005

About CFS
60 Installation and Administration Guide
In addition to file-level frozen images, there are volume-level alternatives available for
shared volumes using mirror split and rejoin. Features such as Fast Mirror Resync and
Space Optimized snapshot are also available. See the VERITAS Volume Manager System
Administrator’s Guide for details.
Synchronizing Time on Cluster File Systems
SFCFS 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.
Distributing Load on a Cluster
Because the primary node on the cluster performs all metadata updates for a given file
system, it makes sense to distribute this load by designating different nodes to serve as
primary for each of the cluster file systems in use. Distributing workload in a cluster
provides performance and failover advantages. Because each cluster mounted file system
can have a different node as its primary, SFCFS enables easy load distribution.
For example, if you have eight file systems and four nodes, designating two file systems
per node as the primary is beneficial. The first node that mounts a file system becomes the
primary for that file system.
You can also use the fsclustadm to designate a SFCFS primary. The fsclustadm
setprimary mount point can be used to change the primary. This change to the primary
is not persistent across unmounts or reboots. The change is in effect as long as one or more
nodes in the cluster have the file system mounted.
A node can be mounted using the mount –seconly option, the result of which the node
does not assume the primary mode for the file system. If a primary node fails and the
remaining nodes are have the file systems mounted as secondary-only, the file system is
disabled. The mount –seconly option overrides the fsclustadm command. See the
mount_vxfs(1M) man page for details on the –seconly option.
Note that recovery for the primary takes more time than the secondary. Distributing
primaries across the cluster would provide a uniform recovery time in the case of a node
failure.