Practical File System Design with the Be File System

Metadata: A general term referring to information that is about something but not directly part of it. For example, the size of a file is very important information about a file, but it is not part of the data in the file. Journaling: A method of insuring the correctness of file system metadata even in the presence of power failures or unexpected reboots. I-node: The place where a file system stores all the necessary metadata about a file. The i-node also provides the connection to the contents of the file and any other data associated with the file. The term “i-node” (which we will use in this book) is historical and originated in Unix. An i-node is also known as a file control block (FCB) or file record. Extent: A starting block number and a length of successive blocks on a disk. For example an extent might start at block 1000 and continue for 150 blocks. Extents are always contiguous. Extents are also known as block runs. Attribute: A name (as a text string) and value associated with the name. The value may have a defined type (string, integer, etc.), or it may just be arbitrary data. 2.3 The Abstractions The two fundamental concepts of any file system are files and directories.