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The main difference between System V shared memory (shmem) and memory mapped I/O (mmap) is that System V shared memory is persistent: unless explicitly removed by a process, it is kept in memory and remains available until the system is shut down. mmap'd memory is not persistent between application executions (unless it is backed by a file).
A memory-mapped file is a segment of virtual memory [1] that has been assigned a direct byte-for-byte correlation with some portion of a file or file-like resource. This resource is typically a file that is physically present on disk, but can also be a device, shared memory object, or other resource that an operating system can reference through a file descriptor.
In computing, a distributed file system (DFS) or network file system is any file system that allows access from multiple hosts to files shared via a computer network. This makes it possible for multiple users on multiple machines to share files and storage resources.
The master maintains all of the files's metadata, including file names, directories, and the mapping of files to the list of chunks that contain each file's data. The metadata is kept in the master server's main memory, along with the mapping of files to chunks. Updates to this data are logged to an operation log on disk.
Non-Shared Resources (NSR), which is optimised for sequential access. NSR access has historically been easier to use than LSR for batch programs. [12] Distributed File Management (DFM), an implementation of a Distributed Data Management Architecture server, enables programs on remote computers to create, manage, and access VSAM files.
POSIX also provides the mmap API for mapping files into memory; a mapping can be shared, allowing the file's contents to be used as shared memory. Linux distributions based on the 2.6 kernel and later offer /dev/shm as shared memory in the form of a RAM disk , more specifically as a world-writable directory (a directory in which every user of ...
In computing, the Global File System 2 (GFS2) is a shared-disk file system for Linux computer clusters. GFS2 allows all members of a cluster to have direct concurrent access to the same shared block storage , in contrast to distributed file systems which distribute data throughout the cluster.
[1] [2] A distributed file system is a protocol that provides file access between networked computers. A file system provides a data storage service that allows applications to share mass storage. Without a file system, applications could access the storage in incompatible ways that lead to resource contention, data corruption and data loss.