Blocks, Files, and Inodes

The different ways of looking at data on a disk can get fairly confusing, but the details are important for understanding how to read the output of tools such as df and fsck. Let’s take a closer look at how storage is divided up and used.

The data block is a unit of data storage; the default size for a data block is 8,192 bytes. A block is divided into eight fragments of 1,024 bytes each. A file that does not take up an entire data block is stored in fragments and shares that block with other files. This process is actually what fsck is referring to when it reports fragmentation.

However, if a file that is currently sharing a data block with another file grows to the point where it will no longer fit in the current block, ...

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