Veritas Storage Foundation 5.0 Cluster File System Administration Guide Extracts for HP Serviceguard Storage Management Suite, Second Edition, May 2008

Technical Overview

Benefits and Applications

Chapter 1

When To Use CFS

You should use CFS for any application that requires file sharing, such as for home

directories, web pages, and for cluster-ready applications. CFS can also be used when

you want highly available standby data in predominantly read-only environments, or

when you do not want to rely on NFS for file sharing.

Almost all applications can benefit from CFS. Applications that are not “cluster-aware”

can operate and access data from anywhere in a cluster. If multiple cluster applications

running on different servers are accessing data in a cluster file system, overall system

I/O performance improves due to the load balancing effect of having one cluster file

system on a separate underlying volume. This is automatic; no tuning or other

administrative action is required.

Many applications consist of multiple concurrent threads of execution that could run on

different servers if they had a way to coordinate their data accesses. CFS provides this

coordination. These applications can be made cluster-aware allowing their instances to

co-operate to balance the client and data access load, and thereby scale beyond the

capacity of any single server. In these applications, CFS provides shared data access,

enabling application-level load balancing across cluster nodes.

• For single-host applications that must be continuously available, CFS can reduce

application failover time, because it provides an already-running file system

environment in which an application can restart after a server failure.

• For parallel applications, such as distributed database management systems and

web servers, CFS provides shared data to all application instances concurrently. CFS

also allows these applications to grow by the addition of servers, and improves their

availability by enabling them to redistribute load in the event of server failure

simply by reassigning network addresses.

• For workflow applications, such as video production, in which very large files are

passed from station to station, CFS eliminates time consuming and error prone data

copying by making files available at all stations.

• For backup, CFS can reduce the impact on operations by running on a separate

server, while accessing data in cluster-shareable file systems.

Some common applications for CFS are:

• Using CFS on file servers

Two or more servers connected in a cluster configuration (that is, connected to the

same clients and the same storage) serve separate file systems. If one of the servers

fails, the other recognizes the failure, recovers, assumes the role of primary node,

and begins responding to clients using the failed server’s IP addresses.

• Using CFS on web servers

Web servers are particularly suitable to shared clustering, because their application

is typically read-only. Moreover, with a client load balancing front end, a Web server

cluster’s capacity can be expanded by adding a server and another copy of the site. A

CFS-based cluster greatly simplifies scaling and administration for this type of

application.