Windows NTFS Introduction to Operating Systems: Module 15

Introduction u FAT family of file systems  FAT12, FAT16, FAT32  Insufficient for networked and corporate environment u NTFS goals  Flexible, secure, and highly reliable u NTFS was not entirely new  Based on another file system : HPFS

Architecture and structures u How information is stored in an NTFS partition  Virtually every structure is, itself, a file except the partition boot sector  Metadata files : set of special files where control information about the partition is stored that are created when an NTFS partition is first created  Every file in an NTFS partition is a collection of attributes, including the data that the file contains  View files as being objects with various characteristics; new attribute if needed in the future can be added u All files are stored using a cluster (extent) system

Architecture and structures u Partition/Volume Boot Sector  Begins in the first sector of the partition  Consists of 2 primary structures : BIOS Parameter Block and Volume Boot Code u BIOS Parameter Block contains  Volume label  Size  Location of key metadata files u Volume Boot Code contains  A small block of program code that instructs the system on how to load the OS – generally load NTLDR, the NT loader program

Example hard disk layout

Architecture and Structures u Metadata files  Placed at the beginning of the partition  Files that contain data about data  Contain internal information about the “real” data stored on the NTFS volume  Master File Table (MFT) : one of the metadata files which contains a record describing every file and directory in an NTFS volume u Master File Table  Most important metadata file  A record is created in the MFT when any file or directory is created

Architecture and Structures u File attributes are stored in MFT record as  Resident attributes  Non-resident attributes u Resident attributes  Stored within the MFT record u Non-resident attributes  Stored either in additional MFT records or in extents that lie outside the MFT u When all file attributes stored within MFT record  No additional storage or separate access to disk required

NTFS Files and Data Storage u Some attributes associated with a file  Header  Standard Information (SI) Attribute –time-stamps, read-only, hidden, and other attributes inherited from FAT  File Name (FN) Attribute – name associated with the file  Data Attribute – actual contents of the file  Security Descriptor (SD) Attribute – security information controlling access to the file (beyond the primitive read-only, hidden, etc. attributes from FAT

How data is stored in files u Store entire file in MFT entry if possible u If not fit, data attribute is made non-resident  Entry for data attribute in MFT contain pointers to data runs (extents)  Data runs – blocks of data stored in contiguous section of the volume, outside MFT u No room for list of pointers in the data attribute  List of data attributes pointers is itself made non-resident  No data attribute in the main MFT; a pointer is placed in the main MFT record to a second MFT record u Multiple non-resident MFT records can be created for very large files – more complex

How data is stored in files u Data runs are where most file data in an NTFS volume is stored  Pointers in the data attribute(s) contain a reference to the start of the extent, and also the number of clusters in the extent  The start of each run is identified using a virtual cluster number (VCN)  Not necessary to read each cluster in order to determine where the next one is located  Reduces fragmentation of files

NTFS performance u NTFS advantages  Best for use on volumes of about 400 MB or more  The recoverability designed into NTFS is such that a user should never have to run any sort of disk repair utility on an NTFS partition  Very quick access to small files u NTFS disadvantages  Not recommended for use on volume that is smaller than approximately 400MB  Not possible to format a floppy disk. Overhead involved in NTFS will not fit onto a floppy disk