j.tiberghien chapitre 9 organisation des disques et gestion des fichiers

J.Tiberghien

Chapitre 9

Organisation des disques

et gestion des fichiers

J.Tiberghien

Disk organization& File

Management• Physical data recording on magnetic disks• Physical organization of data on magnetic disks• Logical disk organization

– Contiguous blocks

– Random blocks: MS/DOS, UNIX, MS/NT

• Directories• System Calls

J.Tiberghien

Disk organization& File

Management• Physical data recording on magnetic disks• Physical organization of data on magnetic disks• Logical disk organization

– Contiguous blocks

– Random blocks: MS/DOS, UNIX, MS/NT

• Directories• System Calls

J.Tiberghien

Writing on magnetic memories

i

0 0 0 0 011 11

J.Tiberghien

Manchester Code

0 00 0 1 11 11i

t

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Reading from magnetic memory

e

0 0 0 0 011 11 0 0 0 0 011 11

J.Tiberghien

Data blocks

Header Data Block Check

0101010101...010101XXXXXXXXX

Check = f(data block)

Synchronization sequence

J.Tiberghien

Disk organization& File

Management• Physical data recording on magnetic disks• Physical organization of data on magnetic disks• Logical disk organization

– Contiguous blocks

– Random blocks: MS/DOS, UNIX, MS/NT

• Directories• System Calls

J.Tiberghien

Disk Organization

Sector

Track

Cylinder

J.Tiberghien

Tracks/cylinder

Cylinders

Sectors/track

Bytes/sector

Total Capacity(in bytes)

Double Density

2

80

9

512

737 280

High density

2

80

18

512

1 474 560

Format of 3.5” diskettes for PC’s.

Sectors/Cluster 2 1

J.Tiberghien

Tracks/cylinder

Cylinders

Sectors/track

Bytes/sector

Total Capacity(in bytes)

15

899

62

512

428 067 840

Format of 428 MBytes Hard Disk.

Sectors/Cluster (16 bit fat) 16

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Minimum Cluster Size(with a 16 bit FAT)

Disk Size

128 MB256 MB512 MB

1 GB2 GB4 GB

Cluster Size

2 kB4 kB8 kB

16 kB32 kB64 kB

Sectors/Cluster

48

163264

128

J.Tiberghien

Space lost to Slack

Block Size Used Space “Slack”

(Bytes) (MBytes) (%)

1 775.2 0.0

512 828.7 6.9

1024 866.5 11.8

2048 948.5 22.4

4096 1128.3 45.6

J.Tiberghien

Disk organization& File

Management• Physical data recording on magnetic disks• Physical organization of data on magnetic disks• Logical disk organization

– Contiguous blocks

– Random blocks: MS/DOS, UNIX, MS/NT

• Directories• System Calls

J.Tiberghien

Mapping the Files on the Disk

• Contiguous Block Allocation– When throughput is critical– When almost no file creation or deletion– Regular space reorganizations required

• Random Block Allocation– When disk space is critical– When lots of file creations and deletions– Disk space optimizations beneficial for

performance

J.Tiberghien

Contiguous Block Allocation

FreeF7F1 F5F3.1F3F2 F6F4

Del F1, F5

F8Save F8

Sorry, Insufficient Disk Space !

Pack

FreeF7Free FreeF3.1F3F2 F6F4

FreeF7F6F3F2 F4

Save F8

F8 FreeF7F6F3F2 F4

J.Tiberghien

Mapping the Files on the Disk

• Contiguous Block Allocation– When throughput is critical– When almost no file creation or deletion– Regular space reorganizations required

• Random Block Allocation– When disk space is critical– When lots of file creations and deletions– Disk space optimizations beneficial for

performance

J.Tiberghien

File Access Table

(MS/DOS)

DISK

FAT

Cluster 0

Cluster x

One entry per Logical Cluster Number

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Conceptual FAT model

Stream a

Stream b

Stream c

Stream d

...

Free

8 12 13

0 1 2 9 10

3 54

1615 17 18 19 ...

6 7 11 14 ...

VCN = 0 1 2 3

LCN

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Partial view of FATDirectory Pointer LCN FAT contents Disk contents

Stream a > 0 1 Stream a, cluster 01 2 Stream a, cluster 12 9 Stream a, cluster 2

Stream b > 3 4 Stream b, cluster 04 5 Stream b, cluster 15 END Stream b, cluster 2

Free Space > 6 7 Free7 11 Free

Stream c > 8 12 Stream c, cluster 09 10 Stream a, cluster 310 END Stream a, cluster 411 14 Free12 13 Stream c, cluster 113 END Stream c, cluster 214 23 Free

Stream d > 15 16 Stream d, cluster 016 17 Stream d, cluster 117 18 Stream d, cluster 218 19 Stream d, cluster 3... ... ...

J.Tiberghien

UNIX Inode

Logical clustersof data on disk

(up to 256)

...256

...256

...256

Logical clusters of data on disk(up to 256*256)

...256

10 Logical clustersof data on disk

...256

...256

...256

...256

...256

...256

...256

Logical clusters of data on disk(up to 256*256*256)

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VCN to LCN mapping in MS/NT

startingVCN

startingLCN

no.ofclusters

0 1355 4

4 1588 5

VCN=

LCN=

0 1 2 3

1355 1356 1357 1358

4 5 6 7 8

1588 1589 1590 1591 1592

J.Tiberghien

Disk organization& File

Management• Physical data recording on magnetic disks• Physical organization of data on magnetic disks• Logical disk organization

– Contiguous blocks

– Random blocks: MS/DOS, UNIX, MS/NT

• Directories• System Calls

J.Tiberghien

Directory Tree

\

info

ex

1k 2k asti 3E

\info\ex\3E

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MS/DOS Directory Entry

bit 0: read onlybit 1: hiddenbit 2: system filebit 3: volume labelbit 4: subdirectorybit 5: archive bit

Base NameExtensionAttributes

Time of creationDate of creationStarting FAT entryFile size

8 bytes3 bytes1 byte

2 bytes2 bytes2 bytes4 bytes

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Unix Directories

\

info

ex

3E

\info\ex\3E

txt

\txt\new

new

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MS/NT Master File Table

SecurityDescriptor

FileName

StandardInformation

Data

1,2 or 4 KBytes

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MS/NT Data Files

SecurityDescriptor

FileName

StandardInformation Actual Data

SecurityDescriptor

FileName

StandardInformation

VCN to LCN mappings

Small file:

Large file:

VCN=

LCN=

0 1 2 3

1355 1356 1357 1358

4 5 6 7 8

1588 1589 1590 1591 1592

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MS/NT Directories

SecurityDescriptor

FileName

StandardInformation

Index of files in MFTf1,f2,f3

Small directory:

Large directory (organized as a Btree):

SecurityDescriptor

FileName

StandardInformation

VCN to LCN mappings + bitmap

VCN=

LCN=

0 1 2 3

1355 1356 1357 1358

4 5 6 7

1588 1589 1590 1591

f1 f2 f4 f5 f6

f3 f7

8 9 10 11

1648 1649 1650 1651

f8 f9

J.Tiberghien

Disk organization& File

Management• Physical data recording on magnetic disks• Physical organization of data on magnetic disks• Logical disk organization

– Contiguous blocks

– Random blocks: MS/DOS, UNIX, MS/NT

• Directories• System Calls

J.Tiberghien

System Calls

File Manipulation

• create file, delete file

• open, close

• read, write, reposition

• get file attributes, set file attributes