Cluster File System Benefits and Applications

Advantages to Using CFS

CFS simplifies or eliminates system administration tasks that result from hardware limitations:

• The CFS single file system image administrative model simplifies administration by making all file system management operations, except resizing and reorganization (defragmentation), independent of the location from which they are invoked.
• You can create and manage terabyte-sized volumes, so partitioning file systems to fit within disk limitations is usually not necessary.
• CFS can support file systems with up to 256 terabyte in size, so only extremely large data farms must be partitioned because of file system addressing limitations.
• Because all servers in a cluster have access to CFS cluster-shareable file systems, keeping data consistent across multiple servers is automatic. All cluster nodes have access to the same data, and all data is accessible by all servers using single server file system semantics.
• Because all files can be accessed by all servers, applications can be allocated to servers to balance load or meet other operational requirements. Similarly, failover becomes more flexible because it is not constrained by data accessibility.
• Because each CFS file system can be the primary on any cluster node, the file system recovery portion of failover time in an n-node cluster can be reduced by a factor of n by distributing the primaryship of file systems uniformly across cluster nodes.
• Enterprise RAID subsystems can be used more effectively because all of their capacity can be mounted by all servers, and allocated by using administrative operations instead of hardware reconfigurations.
• Larger volumes with wider striping improve application I/O load balancing. Not only is the I/O load of each server spread across storage resources, but with CFS shared file systems, the loads of all servers are balanced against each other.
• Extending clusters by adding servers is easier because each new server's storage configuration does not need to be set up---new servers simply adopt the cluster-wide volume and file system configuration.
• The clusterized Oracle Disk Manager (ODM) feature that makes file-based databases perform as well as raw partition-based databases is available to applications running in a cluster.

When to Use CFS

You should use CFS for any application that requires the sharing of files, such as for home directories and boot server files, Web pages, and for cluster-ready applications. CFS is also applicable when you want highly available standby data, in predominantly read-only environments where you just need to access data, 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 on and access data from anywhere in a cluster. If multiple cluster unaware 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. Such applications can be made cluster-aware allowing their instances to co-operate to balance client and data access load, and thereby scale beyond the capacity of any single server. In such 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, the CFS eliminates time consuming and error prone data copying by making files available at all stations.
• For backup, the CFS can reduce the impact on operations by running on a separate server, accessing data in cluster-shareable file systems.

The following are examples of applications and how they might work with the CFS:

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 primaryship, 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.