chapter 5 input/output - folk.uio.nofolk.uio.no/inf242/foils/filesystems.pdf · 1 1 input/output...

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Input/Output

Chapter 5

5.1 Principles of I/O hardware5.2 Principles of I/O software5.3 I/O software layers5.4 Disks5.5 Clocks5.6 Character-oriented terminals5.7 Graphical user interfaces5.8 Network terminals5.9 Power management

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Memory-Mapped I/O (1)

• Separate I/O and memory space• Memory-mapped I/O• Hybrid

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Memory-Mapped I/O (2)

(a) A single-bus architecture(b) A dual-bus memory architecture

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Direct Memory Access (DMA)

Operation of a DMA transfer

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Interrupts Revisited

How interrupts happens. Connections between devices and interrupt controller actually use interrupt lines on the bus rather than dedicated wires

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DisksDisk Hardware (1)

Disk parameters for the original IBM PC floppy disk and a Western Digital WD 18300 hard disk

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Disk Hardware (2)

• Physical geometry of a disk with two zones• A possible virtual geometry for this disk

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Disk Hardware (3)

• Raid levels 0 through 2 • Backup and parity drives are shaded

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Disk Hardware (4)

• Raid levels 3 through 5• Backup and parity drives are shaded

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Disk Hardware (5)

Recording structure of a CD or CD-ROM

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Disk Hardware (6)

Logical data layout on a CD-ROM

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Disk Hardware (7)

• Cross section of a CD-R disk and laser– not to scale

• Silver CD-ROM has similar structure– without dye layer– with pitted aluminum layer instead of gold

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Disk Hardware (8)

A double sided, dual layer DVD disk

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Disk Formatting (1)

A disk sector

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Disk Formatting (2)

An illustration of cylinder skew

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Disk Formatting (3)

• No interleaving• Single interleaving• Double interleaving

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Disk Arm Scheduling Algorithms (1)

• Time required to read or write a disk block determined by 3 factors

1. Seek time

2. Rotational delay

3. Actual transfer time

• Seek time dominates

• Error checking is done by controllers

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Disk Arm Scheduling Algorithms (2)

Shortest Seek First (SSF) disk scheduling algorithm

Initialposition

Pendingrequests

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Disk Arm Scheduling Algorithms (3)

The elevator algorithm for scheduling disk requests

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Error Handling

• A disk track with a bad sector• Substituting a spare for the bad sector• Shifting all the sectors to bypass the bad one

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Stable Storage

Analysis of the influence of crashes on stable writes

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File Systems

Chapter 6

6.1 Files 6.2 Directories 6.3 File system implementation 6.4 Example file systems

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Long-term Information Storage

1. Must store large amounts of data

2. Information stored must survive the termination of the process using it

3. Multiple processes must be able to access the information concurrently

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File Naming

Typical file extensions.

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File Structure

• Three kinds of files– byte sequence– record sequence– tree

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File Types

(a) An executable file (b) An archive

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File Access• Sequential access

– read all bytes/records from the beginning

– cannot jump around, could rewind or back up

– convenient when medium was mag tape

• Random access– bytes/records read in any order

– essential for data base systems

– read can be …• move file marker (seek), then read or …

• read and then move file marker

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File Attributes

Possible file attributes

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File Operations

1. Create

2. Delete

3. Open

4. Close

5. Read

6. Write

7. Append

8. Seek

9. Get attributes

10.Set Attributes

11.Rename

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An Example Program Using File System Calls (1/2)

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An Example Program Using File System Calls (2/2)

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Memory-Mapped Files

(a) Segmented process before mapping files into its address space

(b) Process after mapping existing file ��� into one segment

creating new segment for ���

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DirectoriesSingle-Level Directory Systems

• A single level directory system– contains 4 files– owned by 3 different people, A, B, and C

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Two-level Directory Systems

Letters indicate ���� of the directories and files

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Hierarchical Directory Systems

A hierarchical directory system

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A UNIX directory tree

Path Names

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Directory Operations

1. Create

2. Delete

3. Opendir

4. Closedir

5. Readdir

6. Rename

7. Link

8. Unlink

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File System Implementation

A possible file system layout

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Implementing Files (1)

(a) Contiguous allocation of disk space for 7 files(b) State of the disk after files and � have been removed

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Implementing Files (2)

Storing a file as a linked list of disk blocks

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Implementing Files (3)

Linked list allocation using a file allocation table in RAM

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Implementing Files (4)

An example i-node

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Implementing Directories (1)

(a) A simple directoryfixed size entriesdisk addresses and attributes in directory entry

(b) Directory in which each entry just refers to an i-node

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Implementing Directories (2)

• Two ways of handling long file names in directory– (a) In-line– (b) In a heap

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Shared Files (1)

File system containing a shared file

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Shared Files (2)

(a) Situation prior to linking

(b) After the link is created

(c)After the original owner removes the file

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Disk Space Management (1)

• Dark line (left hand scale) gives data rate of a disk• Dotted line (right hand scale) gives disk space efficiency• All files 2KB

Block size

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Disk Space Management (2)

(a) Storing the free list on a linked list(b) A bit map

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Disk Space Management (3)

(a) Almost-full block of pointers to free disk blocks in RAM- three blocks of pointers on disk

(b) Result of freeing a 3-block file(c) Alternative strategy for handling 3 free blocks

- shaded entries are pointers to free disk blocks

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Disk Space Management (4)

Quotas for keeping track of each user’s disk use

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File System Reliability (1)

• A file system to be dumped– squares are directories, circles are files– shaded items, modified since last dump– each directory & file labeled by i-node number

������������

������ ��

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File System Reliability (2)

Bit maps used by the logical dumping algorithm

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File System Reliability (3)

• File system states(a) consistent(b) missing block(c) duplicate block in free list(d) duplicate data block

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File System Performance (1)

The block cache data structures

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File System Performance (2)

• I-nodes placed at the start of the disk• Disk divided into cylinder groups

– each with its own blocks and i-nodes

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Log-Structured File Systems

• With CPUs faster, memory larger– disk caches can also be larger– increasing number of read requests can come from cache– thus, most disk accesses will be writes

• LFS Strategy structures entire disk as a log– have all writes initially buffered in memory– periodically write these to the end of the disk log– when file opened, locate i-node, then find blocks

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Example File SystemsCD-ROM File Systems

The ISO 9660 directory entry

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The CP/M File System (1)

Memory layout of CP/M

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The CP/M File System (2)

The CP/M directory entry format

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The MS-DOS File System (1)

The MS-DOS directory entry

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The MS-DOS File System (2)

• Maximum partition for different block sizes• The empty boxes represent forbidden combinations

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The Windows 98 File System (1)

The extended MOS-DOS directory entry used in Windows 98

�����

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The Windows 98 File System (2)

An entry for (part of) a long file name in Windows 98

Bytes

Checksum

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The Windows 98 File System (3)

An example of how a long name is stored in Windows 98

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The UNIX V7 File System (1)

A UNIX V7 directory entry

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The UNIX V7 File System (2)

A UNIX i-node

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The UNIX V7 File System (3)

The steps in looking up �������������