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LSBU- Operating systems > Lecture 11 (unfinished) > Flashcards

Lecture 11 (unfinished) Flashcards

1
Q

What are the 6 disk scheduling algorithms

A 
First Come First Served (FCFS)
Shortest Seek Time First (SSTF)
SCAN
Circular SCAN (CSCAN)
LOOK
CLOOK
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2
Q

Storage Techniques in HPC:

DAS

A

Direct Attached Storage (DAS): Drives are installed

physically in the box

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3
Q

Storage Techniques in HPC:

NAS

A

Network Attached Storage (NAS): Storage is not
installed physically but reachable via a TCP/IP
network.

File-level access

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4
Q

Storage Techniques in HPC:

SAN

A

Storage Area Network (SAN): A distributed cluster of
storage. Needs a specific Storage-Specific switch
(typically Fiber- switch)

Block-level access

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5
Q

What is file-level access?

A

Easy to implement
Stores data in files and folders
Less Expensive
Suitable for mass storage

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6
Q

What is block level access

A

Better performance
Can treat each block as an independent disk
More reliable
Can support external boot-up over network

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7
Q

What does RAID stand for?

A

RAID : Redundant Array of Independent Disks

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8
Q

Software RAID vs Hardware RAID

A

Software:

  • Lower cost
  • Support of disk duplexing

Hardware:

  • Faster and more reliable
  • Processing load in on the dedicated controller, not on the OS
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9
Q

What is RAID 0 (disk-striping )

A
  • 2 disks needed
  • Does not support Fault Tolerance (FT)
  • Only supports load balancing in both read and write
  • 100% Capacity
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10
Q

What is RAID 1 (disk-mirroring)

A

• 2 disks or even number of disks needed
• Supports FT by mirroring primary disk to the backup
one.
• 50% utilization

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11
Q

What is RAID 5 (Disk-striping with parity)

A

• 3 disks needed
• Data is stripped into primary disk and backup is stored as parity bits
• Uses Hamming Code for Error Correction
• More complex in utilization, typically needs dedicated
RAID controller
• 1/n Capacity loss
• More expensive than RAID 1

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12
Q

What is RAID 6 ()

A

• Similar to RAID5 but with a backup parity to
support extremely high availability
• 2/n Capacity loss

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13
Q

What is RAID 10

A

• Striping (RAID 0) + Mirroring (RAID 1)

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14
Q

What are files?

A

Data collections created by users

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15
Q

What are 3 Desirable properties of files:

A

Long-term existence
 Files are stored on disk or other secondary storage and do not disappear when a user logs off

Shareable between processes
 Files have names and can have associated access permissions that permit controlled sharing

Structure Structure
 Files can be organized into hierarchical or more complex structure to reflect the relationships
among files

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16
Q

What does the file management system do?

A

 Meet the data management needs of the user
 Guarantee that the data in the file are valid
 Optimize performance
 Provide I/O support for a variety of storage device types

17
Q

What are file systems?

A

Is a Data structure located into RAM by the OS and is used to access storage elements

Provide a means to store data organized as files as well as a collection of functions that can be performed on files

18
Q

What are the four terms commonly used when discussing files?

A

Field
Record
File
Database

19
Q

What is a Field?

A

 Basic element of data

 Contains a single value

20
Q

What is a File?

A

 Collection of similar records

 Treated as a single entity

21
Q

What is a Database?

A

 Collection of related data

 Relationships among elements of data are explicit

22
Q

What is a Record?

A

 Collection of related fields that can be treated as a unit by some application program

23
Q

What is Logical I/O?

A

Enables users and applications to access records

Provides general-purpose record I/O capability

Maintains basic data about file

24
Q

What are the 5 different file organization types?

A 
Pile
Sequential
Indexed sequential
Indexed
Hashed
25
Q

What is a Direct/Hashed file?

A

Access directly any block of a known address

Makes use of hashing on the key value

26
Q

Where is a hashed file used?

A

Often used where:
 Very rapid access is required
 Fixed-length records are used
 Records are always accessed one at a time

27
Q

2 examples of Hashed file?

A

Directories

Pricing tables

28
Q

What are the typical operations of a file system?

A 
Typical operations include:
 Create
 Delete
 Open
 Close
 Read
 Write
29
Q

What are the types of operations performed on a directory?

A 
Search
Create files
Delete files
List directory
Update directory
30
Q

What are the 2 issues that arise with file sharing?

A

Access rights

Management of simultaneous access

LSBU- Operating systems (13 decks)

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