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Windows NTFS

Introduction to Operating Systems: Module 15. Windows NTFS. Introduction. FAT family of file systems FAT12, FAT16, FAT32 Insufficient for networked and corporate environment NTFS goals Flexible, secure, and highly reliable NTFS was not entirely new Based on another file system : HPFS.

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Windows NTFS

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  1. Introduction to Operating Systems: Module 15 Windows NTFS

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

  3. Architecture and structures • 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 • All files are stored using a cluster (extent) system

  4. Architecture and structures • Partition/Volume Boot Sector • Begins in the first sector of the partition • Consists of 2 primary structures : BIOS Parameter Block and Volume Boot Code • BIOS Parameter Block contains • Volume label • Size • Location of key metadata files • 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

  5. Example hard disk layout

  6. Architecture and Structures • 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 • Master File Table • Most important metadata file • A record is created in the MFT when any file or directory is created

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

  8. NTFS Files and Data Storage • 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

  9. How data is stored in files • Store entire file in MFT entry if possible • 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 • 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 • Multiple non-resident MFT records can be created for very large files – more complex

  10. How data is stored in files • 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

  11. NTFS performance • 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 • 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

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