A shared disk file system, also known as cluster file system or SAN file system, is an enterprise storage file system which can be shared (concurrently accessed for reading and writing) by multiple computers. Such devices are usually clustered servers, which connect to the underlying block device over an external storage device. Such a device is commonly a storage area network (SAN). Shared disk file systems are necessary because with regular file systems, if multiple instances were to attempt concurrent access to the same physical device, the data would rapidly become corrupt, because there is nothing to prevent two devices from performing a modification of the same part of the file system at the same time. Conventional file locking is no aid in this, as it operates above the file system level; it can protect files against concurrent access but offers no protection of the file system itself. A shared file system extends the file system concept by adding a mechanism for concurrency control. It provides each device accessing the file system with a consistent and serializable view of the file system, avoiding corruption and [unintended] data loss. Such file systems also usually employ some sort of a fencing mechanism to prevent data corruption in case of node failures. There are different architectural approaches to a shared disk file system. Some distribute file information across all the servers in a cluster (fully distributed). Others utilize a centralized metadata server. Both achieve the same result of enabling all servers to access all the data on a shared storage device. Examples of such file systems include:
Compare
- SAN file systems are similar to network attached storage (NAS) protocols (like SMB and NFS) in that they allow multiple computers to access the same file system (and even file) at the same time, but unlike them, they require simultaneous physical access to the storage device to all computers in the cluster.
- Distributed file system, different approach
