File System Structures

1. File System Structures

• Purpose: Efficient access to disk, storing, locating, and retrieving data.

• Layering Approach: Different layers handle specific tasks.

  1. Logical File System:
     • Handles file metadata and directory structure.
     • Verifies file path and permissions.
  2. File Organization Module:
     • Maps logical blocks to physical blocks.
     • Manages free space.
  3. Basic File System:
     • Issues commands to I/O control for block fetching.
  4. I/O Control:
     • Accesses hard disk via device drivers.
     • Handles interrupts.

2. File System Operations

• Create: Initializes a file with no data.
• Open: Prepares a file for other operations.
• Read: Accesses data within a file, managed by a read pointer.
• Write: Adds data to a file and repositions the file pointer.
• Reposition (Seek): Moves file pointer to a specific position.
• Truncate: Deletes file data without releasing disk space.
• Delete: Removes file and frees disk space.
• Rename: Changes the file's name.
• Append: Adds data to the end of a file.
• Close: Closes the file, releasing resources and saving changes.

3. Storage Structures in Operating Systems

• Storage Hierarchy: Balance between speed, cost, and capacity.
  • Registers: Fastest, smallest, used by CPU for quick access.
  • Cache Memory: Temporary storage for frequently accessed data.
  • Main Memory (RAM): Primary storage, larger but slower than cache.
  • Virtual Memory: Extends memory using hard disk space.
  • Secondary Storage: Stores data/programs not in use (e.g., HDDs, SSDs).
  • Tertiary Storage: Long-term storage (e.g., tape drives).

4. Flash Memory / Flash Storage

• Definition: Nonvolatile, high-speed, electrically programmable memory.
• Types:
  • NAND Flash: Optimized for high-density storage, serial access.
  • NOR Flash: Optimized for random access, parallel connections.
• Examples: SSDs, USB drives, MMC, BIOS chips.
• Applications: Widely used in consumer devices, industrial applications, and enterprise systems.

5. Flash Storage Optimization

• Enable TRIM: Helps manage data blocks efficiently.
• Firmware Updates: Improve performance and reliability.
• Wear Leveling: Distributes write/erase cycles evenly.
• Over-Provisioning: Reserves space to maintain performance and lifespan.
• Optimal File System: Use file systems like NTFS, exFAT, APFS.
• Avoid Full Capacity: Keep 10-20% free space.
• Avoid Unnecessary Writes: Minimize swap files and relocate temp files.
• Temperature Management: Maintain recommended temperature range.
• Regular Backups: Protect data against unexpected issues.
• Check for Disk Errors: Use built-in tools for timely error detection.
• Selective Indexing: Limit indexing to essential directories to reduce writes.