Operating System Concepts and

Techniques Lecture 18

Information management-2*FFS, UFS2, NTFS

M. Naghibzadeh

ReferenceM. Naghibzadeh, Operating System Concepts and Techniques, First ed., iUniverse Inc., 2011.

To order: www.iUniverse.com, www.barnesandnoble.com, or www.amazon.com

* Information management is not usually covered in the first course of operating systems

Fast file systemLarger block size than UFS

To avoid excess internal fragmentation: A data block is divided into a number of equal size

fragments (often eight). These fragments can be independently assigned to files and directories

Since UNIX frequently has many small files and directories, most of the time these are placed in the

fragments left over by larger directories and files In the file’s or directory’s i-node eight bits are

reserved to show which segments of the last data block is occupied by this file

A one means it is used and a zero means otherwise

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Fast file system...Based on UFS

Data blocks of a file or directory are stored in cylinders that are placed as close as possible to

each other A number of adjacent cylinders are called a cylinder

group The on-disk i-node of a file or directory is stored in

the same cylinder group of the file or directory Data blocks of directories are distributed across the

whole disk’s data area so that a directory’s data blocks are close to its files data blocks

Furthermore, a file’s and directory’s on-disk i-node is stored as close as possible to the file’s or directory’s

data blocks

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Fast file system...Other improvements:

The Berkeley FFS has two superblocks instead of one. If one of the superblocks becomes

faulty the system immediately switches to the other and starts repairing

Another FFS enhancement is the increase in the file name’s length to 255 characters

Yet another improvement is its two different block sizes, for example, 4K and 8K

For small size files (or directories), the first block size is used and for large size files

there is the second block size.

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FFS adv/disadvAdvantages:

Accessing a directory’s or file’s data is faster because the number of seek times is usually less than that of the original UFS file system

Disk head movements are reduced thus raising overall performance

Superblock failure recovery is possible Can be used with UFS and USF2

Disadvantage: Increases the complexity of the file system

implementation

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UNIX File System 2Based on UFS

Pointers to USF2 data blocks are eight bytes long, one tera byte file can be stored

the size of each i-node is 256 bytes Usually few bunch of consecutive blocks are

assigned, simultaneously Number of pointes is reduced

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NTFS file systemObjectives:

Supporting a wide range of systems; has many versions

Recoverability File system recovery; use of transaction concept

Security and protection File and directories are considered object, must

have the right to access Memories are cleared before allocation

Windows provides the capability to encrypt file information upon the user’s request

Very large files A file can be as large as 264 bytes

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VolumeVolume is a collection of clusters for which a file

system is usedCan be part of a disk, a disk, or a set of parts of

many disksThe maximum size of a volume is 264 bytes

Four general sections are identified in a volume

Like UNIX, files and directories are treated the same

in NTFS, name, attributes, and data of files all called attributes

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Boot sector Master file table Recovery data Attributes and data blocks

Boot sectorOne OS per volume possible, one boot sector

per OSBoot sector (Master Boot Record (MBR) in 32-

bit or GUID (Globally Unique Identifier) Partition Table (GPT) in 64-bit )

512 bytes Very essential metadata of the volume such as, the

number of bytes per sector, the number of sectors per cluster, disk type (floppy, hard), the number of

sectors per record, the location of master file tables, disk identification, and whether the volume is

bootable or not A small machine language program

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NTFS Boot Sector0x00 3B Jump Instruction

0x03 8B OEM-ID (original equipment manufacturer-id)

0x0B 25B BPB (BIOS Parameter Block)*0x24 48B Extended BPB*

0x54 426B Bootstrap Code. 0x1FE 2B End of Sector Marker

* 0x0B, Bytes per sector.

0x0D Sectors per Cluster

0x15 Media descriptor. F8: HD; F0: HD Floppy

0x28 Total sectors.

0x30 Logical cluster number for the MFT

0x38 Logical cluster number copy of the MFT

0x40 Clusters per MFT Record.

0x48 Volume serial

NTFS Master File TableInformation on how to find files and directories

attributes and dataA record based file; each record is 1K

There is at least one record for each file (or directory) called base record

A file’s entire metadata may not fit in one record; in such case, extended records are allocated

A file of variable sizeNot all attribute names are applicable to all filesFirst 16 records are reserved for metadata files,

their name begins with $First four entries are replicated for MFT repair

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Master File Table

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$Mft Master file table $MftMirr Mirror copy of Mft $LogFile Log file for recovery $Volume Volume file $AttrDef Attribute definition $ Root directory $Bitmap Bitmap of clusters used $Boot Bootstrap loader $BadClus List of bad clusters $Secure Security descriptors of files $Upcase Case conversion table $Extend Extension: quotas, etc Reserved for future use Reserved for future use Reserved for future use Reserved for future use A User file A User file . . .

0123456789101112131415...

System files

User filesand system and user

files extensions

1K

An MFT recordDifferent sections of a MFT record

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Some metadata Other MFT records for this file File data clusters Unused

ExampleExample: Suppose a file’s data is stored in

cluster numbers 501, 502, 503, 585, 586, 587, 588, 589, 621, 622, 623, 624, 625, 674, 675,

676, 677, 678, 690, and 691How this information is stored in the file’s base

and extended MFT records?If each set of adjacent clusters is called a

bunch, then this file’s clusters will form five bunches: 501 to 503, 585 to 589, 621 to 625,

674 to 678, and 690 to 691Suppose also that two MFT records are needed

to save the attributes of this file

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Example…The first record is the base record with record

number sya 125 and the second one is an extended record with record number say 482

Roughly speaking, the information shown in the figure above is stored in the base record of

this fileThe information in the figure below is stored in

the extended record of this file

Headers are delimeters

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Headers and file attributes Header 482 Header 501 3 583 5 621 5

Headers 674 4 690 2 Free space

Accessing a file and its data

Suppose the following figure is the structure of the files and directories of the specific volume

in which file K’s data is to be located

The absolute path of the file is /C/R/KD

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B C

RSWX

A D

P

Q L K

Directory

File

Accessing a file and its data...

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Root directory is stored in record number 5 of MFTSuppose root’s data are stored in say cluster no. 950

Cluster number 950 is accessed, the information is the names and base MFT records of the root directory’s files

and directoriesA sequential or B+ search locates C and its base MFT

record is 125This record is accessed just as C was searched for with record 5 replaced by 125 and C replaced by R, suppose

record 85 is the base MFT record for RNow, K must be found; suppose this is done and the

base MFT record 94 is extracted for file KFrom this base record and its extensions, all metadata

and data of file K can be located

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NTFS SummaryBerkeley Fast File System was briefly discussedUNIX File System 2 was also briefly introduced

The design details of New Technology File System was studied

Each file on an NTFS volume is represented by a record in a special file called the master file

table (MFT)The first 16 records of MFT are for special filesEach file and directory has a base MFT record and zero or more extended record to store its

metadataDirectories are also viewed as files by NTFS

An example was presented to show how a file’s metadata and data are stored and how we can

locate a file or directory

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Find outThe advantages of UFS2 over USF

The detailed information stored in base MFT record

What is the purposes of record numbers 12, 13, 14, and 15 of the MFT file

The maximum size of a file whose metadata and data can completely fit in its base MFT record

The purposes of record number four of MFT fileHow we can use two disks as one volume

Which records of the MFT file are duplicatedThe purposes of duplicating some records of the

MFT file

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Any questions?