Question

Consider a file systemthat uses a modifiedcontiguous-allocation scheme with support for extents.A file is a collection of extents, with each extent corresponding to a contiguous set of blocks. A key issue in such systems is the degree of variability in the size of the extents. What are the advantages and disadvantages of the following schemes? a. All extents are of the same size, and the size is predetermined. b. Extents can be of any size and are allocated dynamically. c. Extents can be of a few fixed sizes, and these sizes are predetermined.

(Operating System , CSE)

Answer 1

a. All extents are of the same size, and the size is predetermined.

• If all extents are of the same size, and the size is predetermined, then it simplifies the block allocation scheme.
• A simple bit map or free list for extents would suffice.

b. Extents can be of any size and are allocated dynamically.

• If the extents can be of any size and are allocated dynamically, then more complex allocation schemes are required.
• It might be difficult to find an extent of the appropriate size and there might be external fragmentation.
• Very complex.

c.Extents can be of a few fixed sizes, and these sizes are predetermined.

• If the extents can be of a few fixed sizes, and these sizes are predetermined, one would have to maintain a separate bitmap or free list for each possible size.
• This scheme is of intermediate complexity and of intermediate flexibility in comparison to the earlier schemes.

Thank you.