Terminology and Basic Principles
Magma binds several hosts interconnected by a TCP/IP network to form a common storage space called a lava ring. Each host (or node) is called a vulcano. Each vulcano hosts a portion of a common key space, delimited by two SHA1 keys. Each vulcano is also in charge of mirroring the key space of the previous node, to ensure data redundancy. Each key can represent one or more object inside the storage space. These objects are called flares.
Magma can store a different range of objects: files, directories, symbolic links, block and characted devices, FIFO pipes. Each object is bound to a flare and vice versa. A flare of any type in the six listed above is described by some basic properties common to all flares, like a path and a hash key. But each of the six types has also its own specific properties. For example, directory flares will have some specific information that don't apply to symbolic links. A flare with only generic information is called uncast while a complete flare is called cast.
An uncast flare does not contain enough information to operate on data, but has enough information to be moved as a sort of opaque container between vulcano nodes. To be easily movable, each type of flare, including directories, has been reimplemented as a two files set, the first containing flare information (metadata) and the second containing flare content. Moving flares across lava ring is called load balancing and is done to leverage load inequalities between nodes in the attempt to provide best performance.
Read more about this topic: Magma FS
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