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Root ObjectContainer
Administration space

Block format

SFS has two Root blocks, one at the start and one at the end of the disk.  The Root blocks both contain the same information.  They hold various information about the disk structure and have the locations of some important blocks used by the filesystem.   (You can click on the picture to see parts of it in more detail).

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The Root ObjectContainer contains the Root directory Object.  The name of this Object is the name of the volume.  It is identical to a normal directory Object.

The Bitmap is used to keep track of free space.  Each bit in a bitmap represents a single block.  A set bit indicates a free block and a cleared bit a used block.

AdminSpaceContainers are used to keep track of space which has been reserved for storing administration blocks.  Only the Bitmap, the Root blocks and the actual data stored in files aren't stored in administration space.  Administration space is allocated in chunks of 32 blocks at a time.  A single AdminSpaceContainer can hold information about a large number of such areas each of which has its own little bitmap of 32 bits.

Extents are stored in a B-Tree.  The Root block holds a pointer to the root of the Extent B-Tree.  Extents keep track of space in use by a specific file.  Each fragment a file consists of has its own Extent.  Extents are in a double linked list.   The list can be used to locate the next or previous fragment of a file.

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For comments, problems or questions regarding this page contact John Hendrikx.
Last updated: 17 oktober 1998.