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ser334_unit12_exercise_sample.lyx
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Arizona State University
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SER334: Operating Systems & System Programming
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\noindent
UGTA Lisonbee (5), UGTA Bush (3), Lecturer Acuña (1)
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Revised 4/26/2022
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Unit 12 Sample Problems - Mass-Storage Structure
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(SOLN)
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Overview:
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In this exercise, we will review the concepts of mass-storage structures.
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\begin_layout Itemize
Length: 50 minutes with discussion.
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\begin_layout Itemize
Questions: TBD (optional: TBD)
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Learning Objectives:
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\begin_layout Enumerate
Describe the advantages and disadvantages of hard disk drives, solid state
drives, and magnetic tapes.
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name "lo:describe-advan-disadvan-hdd-ssd-mt"
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name "lo:describe-storage-infrastructures"
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Produce a trace of major disk scheduling algorithms (e.g., FCFS, SSTF, SCAN,
C-SCAN, LOOK).
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name "lo:trace-disk-scheduler"
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Determine the appropriate RAID configuration for a data access need.
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Background
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[Lisonbee] Hard disk drives, solid state drives, and magnetic tape all are
very different solutions to the same problem.
Knowing that SSDs don't rely on moving parts to read data, what is the
most significant advantage they have over HDDs and MT in terms of how the
data is distributed over the medium?
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Explain
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.
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Ans: [Lisonbee]
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SSDs provide uniform memory access, meaning that every piece of data stored
on the drive can be accessed equally fast.
This is different from HDDs and MT because both of those storage mediums
rely on moving parts that read data.
HDDs have heads that track along the platters, and the closer to the center
of the disk they read from, the slower the read speeds are (assuming constant
angular velocity).
MT is even worse than HDDs in this regard as it has to read the data linearly.
If a piece of data needs to be read is on the complete opposite end of
the tape, then it has to track all the way to the other end to get that
data.
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Disk Structure
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[Lisonbee] Consider a single platter of a hard disk drive.
If you assume the platter has a uniform data density across the entire
platter, and that the platter spins with a constant angular velocity, what
happens to the read and write speed as the read-write head tracks across
the platter? What could you change to ensure the read and write speed stays
constant?
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As the read-write head tracks along the platter, the read and write speed
increases or decreases relative to the position of the head.
As the head moves closer to the outside of the platter, the linear velocity
will increase yet the density of data is the same, therefore the read/write
speed increases.
To achieve a constant read/write speed you must either change the data
density on the platter to be non-uniform (less dense toward the outside),
or change the angular velocity depending on the location of the track to
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Disk Attachment
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[Lisonbee] Imagine you are in charge of installing a mass-storage solution
for a new company, and you need to decide what kind of solution would be
best.
The company needs to store large amounts of data, and it needs to be quickly
and easily accessible by all of their employees.
They stressed that they want the storage solution to be scalable, so they
can grow it along with the company.
Would a network-attached storage solution or a storage-area network be
a more appropriate choice?
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your reasoning.
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A storage-area network would be the most appropriate choice for this situation
as it is easier to scale by nature, and it wouldn't congest the entire
network when employees are accessing data.
Furthermore, given the company is just starting out, the SAN would provide
greater flexibility with how they manage and allocate their data.
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Disk Scheduling
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[Acuña] Consider using the SSTF disk scheduling algorithm on the cylinder
blocks 18, 43, 70, 55, 27, 33, 58, 44.
What cylinder order would be produced, and how far would the disk head
need to travel? Assume the disk head is initially at 25, and that the disk
has cylinders 1 to 100.
[2 points] [LO
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Ans: [Acuña]
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[Lisonbee] Consider using the FCFS disk scheduling algorithm on the cylinder
blocks 54, 23, 12, 128, 9, 66, 47, 18.
What cylinder order would be produced, and how far would the disk head