Filesystems

1
Filesystems
2
What is Filesystem?

• A method for storing and organizing computer
  files and the data they contain to make it easy
  to find and access them
• File systems may use a data storage device such
  as a hard disk or CD-ROM
• May
• Maintain the physical location of the files
• Provide access to data on a file server by acting
  as clients for a network protocol
• Be virtual and exist only as an access method for
  virtual data

3
Filesystem Basics

• Offer access to an array of fixed-size blocks
  (sectors)?
• Sectors are generally a power of 2 in size(512
  bytes, or 1, 2, or 4KB)?
• Responsible for organizing sectors into files and
  directories
• Keeps track of which sectors belong to which file
  and which are not being used

4
Aspects

• File Names
• Metadata
• Size
• Time
• Permissions
• Hierarchical
• Facilities
• Create, Move, Delete
• Truncate, Append To, In-Pace Modify
• Secure Access (through Access Control Lists)?

5
Types

• Disks
• Flash
• Database
• Transactional
• Network
• Special Purpose

6
Disk Filesystems

• ext
• ext2
• ext3
• FAT (12-, 16, and 32-bit table depths)?
• NTFS (New Technology File System)?

7
ext

• Extended Filesystem
• Created in April 1992 for Linux
• Superseded by ext2
• Allows up to 2 GB of data
• Filename size up to 255

8
ext2

• Created in January 1993 for Linux
• Superseded by both ext2
• Newer versions allow data of gt 2TB
• The space is split up in blocks, and organized
  into block groups
• This is done to reduce external fragmentation and
  minimize the number of disk seeks when reading a
  large amount of consecutive data

9
ext2
10
ext3

• Journaled filesystem
• Created in November 2001 for Linux
• Total size up to 16TB
• At its core, same as ext2

11
FAT

• File Allocation Table
• Created for MS-DOS
• When files are deleted and new files written to
  the media, directory fragments tend to become
  scattered over the entire disk
• Up to 8 TB volume size
• 4GB 1 byte maximum filesize
• 255 character filename limit

12
FAT

• Boot Sector
• Reserved Sector (Optional)?
• FAT 1
• FAT 2
• Root Directory (FAT12/16 only)?
• Data Region

13
NTFS

• Superseded FAT
• Standard FS for Windows NT (and higher)?
• Journaled
• Up to 256 TB volume size
• 16TB 64 KB maximum filesize
• 255 character name limit (there are reserved
  words)?