Filesystem technologies

Three types of filesystem technologies are important for Linux-HA: Journalling filesystems, Cluster filesystems and Mirror filesystems. Journalling filesystems allow takeover of shared/mirrored filesystems to occur rapidly in cases of failover. Cluster filesystems allow disks to be shared read-write between all members of a cluster simultaneously - which is highly desirable for many parallel applications. Mirror filesystems replicate, or mirror, files to multiple remote locations on the network in real time, ensuring that any given file is always up-to-date and always available.

Journalling and Log-structured Filesystems

• Reiserfs: A tree-structured filesystem which journals updates. It is available with most 2.4 and later kernels.

• Ext3: Stephen Tweedie's journalling version of the ext2 filesystem. It is available with most 2.4 and later kernels.

• JFS: IBM's journalled filesystem technology. It is available with many Linux distributions.

• XFS: SGI's journalled filesystem technology.

• LinLogFS: A log structured filesystem for Linux

• Intermezzo: A distributed file system which lets systems replicate directory trees. It is a standard part of 2.4 and later kernels. It isn't precisely what most people would call a cluster filesystem, but it's related.

Cluster Filesystems

• Lustre: Lustre is a novel storage and file system architecture and implementation which does not follow the block device paradigm. The central target in this project is the development of a next-generation cluster file system which can serve clusters with 10,000's of nodes, petabytes of storage, move 100's of GB/sec. Lustre is in trial production in several sites across the world.

• GFS: The Global Filesystem - fault tolerant, distributed, very cool, etc. GFS is both a cluster filesystem and a journalled filesystem.

• The CODA distributed, fault-tolerant filesystem

• Oracle Cluster File System (OCFS): enterprise-class open-source cluster file system

Mirror Filesystems

• MFS: The Mirror File System links and manages file systems on two or more geographically-dispersed machines. When a file is updated, the changed portion is mirrored in real time to a copy residing on a remote location. MFS is a new solution for HA, load balancing, DR, and online file backup built on top of ext3 and NFS. It is completely transparent to users and applications

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