Shared disk file system
SAN Recovery - Shared disk file system
A shared disk file system is a type of enterprise storage file system that can be shared among multiple computers. These computers are collectively called clustered servers, and they connect to the underlying block device over an external storage device known as storage area network. Hence, shared disk file system is also called as clustered file system or SAN file system.
Regular file systems do not have the facility to allow two devices perform a modification of the same part of the file system at the same time. If multiple instances were to attempt concurrent access to the same physical device, data would become corrupt. Conventional file locking can protect files against concurrent access, but it does not offer protection when a server or an operating system manipulates the blocks of storage device.
The shared file system prevents corruption and unintended data loss with the help of a concurrency control mechanism. It provides each device accessing the file system with a consistent view of the file system. These file systems also feature a fencing mechanism to prevent data corruption caused due to node failures.
A shared disk file system can be either fully clustered, meaning they distribute information in clusters; else, they may use a centralized metadata server to distribute file information across all servers. In both cases, the file system enables all servers to access the information on a shared storage device.
To summarize, a shared disk file system is used in storage area network where all nodes directly access the block storage where the file system is located. It is mostly used in high-availability cluster, along with storage on hardware RAID.
