Cluster File Systems

A cluster file system is a proxy between the following:

• The kernel on one node and the underlying file system

• The volume manager running on a node that has a physical connection to the disk or disks

Cluster file systems are dependent on global devices (disks, tapes, CD-ROMs). The global devices can be accessed from any node in the cluster through the same file name (for example, /dev/global/). That node does not need a physical connection to the storage device. You can use a global device the same as a regular device, that is, you can create a file system on a global device by using newfs or mkfs.

The cluster file system has the following features:

• File access locations are transparent. A process can open a file that is located anywhere in the system. Also, processes on all nodes can use the same path name to locate a file.

  ---

  Note –

  When the cluster file system reads files, it does not update the access time on those files.

  ---

• Coherency protocols are used to preserve the UNIX file access semantics even if the file is accessed concurrently from multiple nodes.

• Extensive caching is used with zero-copy bulk I/O movement to move file data efficiently.

• The cluster file system provides highly available advisory file-locking functionality by using the fcntl(2) interfaces. Applications that run on multiple cluster nodes can synchronize access to data by using advisory file locking on a cluster file system file. File locks are recovered immediately from nodes that leave the cluster, and from applications that fail while holding locks.

• Continuous access to data is ensured, even when failures occur. Applications are not affected by failures if a path to disks is still operational. This guarantee is maintained for raw disk access and all file system operations.

• Cluster file systems are independent from the underlying file system and volume management software. Cluster file systems make any supported on-disk file system global.