Access over 35 million academic & study documents

each extent corresponding to a contiguous set of blocks A key issue

Content type
User Generated
Rating
Showing Page:
1/4
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? All extents are
of the same size, and the size is predetermined. Extents
can be of any size and are allocated dynamically. Extents
can be of a few fixed sizes, and these sizes are
predetermined. Contrast the performance of the three
techniques for allocating disk blocks (contiguous, linked,
and indexed) for both sequential and random file access.
What are the advantages of the variant of linked allocation
that uses a FAT to chain together the blocks of a file?
Consider a system where free space is kept in a free-
space list. Suppose that the pointer to the free-space list
is lost. Can the system reconstruct the free-space list?
Explain your answer. Consider a file system similar to the
one used by UNIX with indexed allocation. How many disk
I/O operations might be required to read the contents of a
small local file at/a/b/c? Assume that none of the disk
blocks is currently being cached. Suggest a scheme to
ensure that the pointer is never lost as a result of memory
failure.
Solution
Three widely used allocation techniques are contiguous,
linked and indexed. The first one is contiguous allocation.
The last two belongs to non contiguous allocation of files.
The contiguous disk allocation:

Sign up to view the full document!

lock_open Sign Up
Showing Page:
2/4
The contiguous allocation method requires each
file to occupy a set of contiguous address on the disk. It
stores each file as a contiguous run of disk blocks. That
means disk addresses define a linear ordering on the disk.
Contiguous allocation of file is defined by the disk address
and the length of the first block.
Both sequential and direct access is supported by
the contiguous allocation method.
The difficulty with contiguous allocation is how to
find a space for a new file, if the implementation of a free
space list is done through a bit map method then for the
creation of a n- bytes long file, we need to find n 0 bits in a
row.
The major problem with contiguous allocation is
how to determine the space needed for a file. While this is
not a problem when copying files, accurate estimation of
file size is generally difficult and unreliable.
The advantages of contiguous disk allocation:
Linked allocation
Linked allocation is essentially a disk-based
version of the linked list. With linked list allocation each
file is linked list of disk blocks. These disk blocks may be
scattered through the disk. A few bytes of each disk block
contain the address of the next block. The directory
contains a pointer to the first (and last) blocks of the file.

Sign up to view the full document!

lock_open Sign Up
Showing Page:
3/4

Sign up to view the full document!

lock_open Sign Up
End of Preview - Want to read all 4 pages?
Access Now
Unformatted Attachment Preview
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? All extents are of the same size, and the size is predetermined. Extents can be of any size and are allocated dynamically. Extents can be of a few fixed sizes, and these sizes are predetermined. Contrast the performance of the three techniques for allocating disk blocks (contiguous, linked, and indexed) for both sequential and random file access. What are the advantages of the variant of linked allocation that uses a FAT to chain together the blocks of a file? Consider a system where free space is kept in a free space list. Suppose that the poi nter to the free-space list is lost. Can the system reconstruct the free -space list? Explain your answer. Consider a file system similar to the one used by UNIX with indexed allocation. How many disk I/O operations might be required to read the contents o f a small local file at/a/b/c? Assume that none of the disk blocks is currently being cached. Suggest a scheme to ensure that the pointer is never lost as a result of memory failure. ...
Purchase document to see full attachment
User generated content is uploaded by users for the purposes of learning and should be used following Studypool's honor code & terms of service.

Anonymous
Great! 10/10 would recommend using Studypool to help you study.

Studypool
4.7
Indeed
4.5
Sitejabber
4.4