Homework 5, released on Nov 13, 2000. CS414 Fall 2000 Due in class Nov 21, 2000
Please hand in your answers
as follows: not handwritten (except drawings), 11-pt Times or 10-pt Courier
font, minimum of .5” margins. Problems
must be grouped (1-2, 3-4, 5, 6, 7) on separate sheets of paper (total 5
sheets). Your name and id should be
written on each sheet of paper you submit.
Please write the question numbers in the sheet in bold. Every item is worth 5 points, unless
otherwise marked.
Late homeworks accrue 10%
penalty for the first 24 hours or 15% if handed in before 4pm on
Wednesday. Homeworks will not be accepted after that. Collaboration is permitted in groups of at most 2 people for this
homework. Add both names to answer sheets in case of a group. Late homeworks are to be handed to Tammy
Howe in 4119C.
FILE SYSTEMS
1)
What,
in your expert opinion, is the best way to enhance the performance of
disks? Mention a specific technique,
explain why this is good, and why do you think other techniques will not be
better. For the last part of the
question, you do not have to list all other techniques, you can just talk in
general terms.
2)
Describe
the advantages and disadvantages of AFS with comparison to vanilla Unix, with
respect to protection. Define access lists and protection matrix, mention the
overhead of creating and maintaining them (you need to include a quick
description of an implementation here).
3)
Describe
in at most 3 lines a smart way to do file backups, if you are not concerned
with disk space (assume you have as much disk space as you want). Some interesting examples are the AFS and
VMS systems.
4)
This
question is about Log-structured File System (LFS).
a.
Can
a LFS and a hash table for directory implementation co-exist? Justify your answer.
b.
What
are the differences (if any) between LFS and the swap space partition?
5)
Most
reasonably-sized systems being built are going toward a FS server
implementation, where specialized nodes are responsible for storing and
retrieving data over a reasonably fast network.
a.
Is
100Mbps (mega bytes per second) Ethernet sufficient to support a network of 10
nodes? Justify your answer, which will
be yes, no, or it depends. In
any case, you should add the math used to justify your answers; this includes
the parameters (e.g., what is the size of the packet, time to transmit, etc)
and computations on these parameters.
b.
If
there is plenty of bandwidth in the system, where should the disk-cache be
located (at the server’s main memory, at the client’s main memory, or at the
client’s disk)? Write your assumptions
and justify your answer.
c.
Does
a client-server implementation of a FS impact the disk scheduling
algorithms? Why or why not?
6)
Given
response time as the performance metric,
a.
3 pt BONUS Is there a total
order on the several disk scheduling algorithms that we have studied (FCFS,
SSTF, SCAN, C-SCAN, LOOK)? Total order
here means the ordering the algorithms according to their effectiveness
(performance).
b.
In
particular, is FCFS always worse than SSTF?
For FCFS-SSTF comparison, sketch the proof or show a counter-example.
7)
Suggest
one way to make RAIDs more efficient.
Define your metric.