Development and Implementation of a File System for Gannet Virtual ...

is quite small. Furthermore, the size of data block can be configured to be bigger to
allow storing large files.
2.4.2 Metadata Representation of a Directory
Unix directories are considered as files whose data blocks maintain list of entries.
The list stores the names and inodes id for each file and directory reside within it.
The structure design for the list determines the performance of traversal operation
and fast random lookup to locate a file (Wang et al. 2006).
Thus, the mapping of name to inode numbers on directory is very important. There
are several ways to maintain the name to inode number mapping. Unix-style file
systems use a simple linear list to store the entries of a directory (McKusick et al.
1996). The major advantage is space effective as it is simple to implement. However,
the disadvantage rise when there are considerable amount of files reside in a
directory. This implementation works fine in small number of files, but will
degraded significantly as the number of files increases since the time complexity is
O(n).
Another approach to mapping the name and inode number is to use a B+trees as
implemented on BeFS and also XFS (Sweeney 1996). The data structure stores pairs
of key and value as name and inode number respectively, in a balanced tree
structure. By using B+trees data structure, the time complexity can be reduced to
O(Log n) to look up an item. Furthermore, BeFS and XFS also need B+tree data
structure for indexing the file attributes.
Another approach is used a hashing table (Fagin et al. 1979) as directory
representation. The structure is built by a hierarchy of hash tables, using file names
as keys and inode numbers as values. By using hash table data structure, the time
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