MFS 1.5.12

MFS 1.5.12 is yet another extremely useful utility for everyone. It is actually a networking, distributed file system. It spreads data over several physical localizations (servers), which are visible to a user as one resource. For standard file operations MFS acts as other Unix-alike file systems. It has hierarchical structure (directory tree), stores file attributes(permissions, last access and modification times) and makes it possible to create special files (block and character devices, pipes and sockets), symbolic links (file names pointing to other files accessible locally, not necessarily on MFS) and hard links (different names of files which refer to the same data on MFS).

On a client computer with mounted MFS all file operations are exactly the same as with other file systems. The kernel of the operating system transfers all file operations to the FUSE module, which communicates with the mfsmount process. The mfsmount process communicates through the network subsequently with the managing server and data servers (chunkservers). This process is fully transparent to the user.
mfsmount communicates with the managing server during all operations on metadata files (creating files, deleting files, reading directories, reading and changing attributes, changing sizes and on any access to special files on MFSMETA) and to start reading or writing data. Data is sent through a direct connection to one of the dataservers (chunkservers) which is storing the relevant chunk of a file. After finishing the write process, the managing server receives information to update a file's length and the last modification time.

Thanks to the fact that file data is stored in many copies, the system is resistant to failures of single data servers (chunkservers) or temporary communication outages between them (this of course does not refer to files with the "goal" set to 1). Exceptionally important files may be set to have a number of copies higher than two, in this case these files are resistant even to a breakdown of more servers at once (there should be at least one more copy available than the number of inaccessible or out-of-order servers).
In case of failure or disconnecting the server storing the data of a file which has at least two copies, the data will remain accessible from another server, and later the data will be replicated on another accessible data server (chunkserver) to provide the required number of copies. Please note that if the number of available servers is lower than the "goal" set for a given file or the number of servers is equal to the required number of copies, but there is no free space, the required number of copies can not be preserved. In this case a new server should be connected as soon as possible. Another server can be connected at any time.