File Systems & Storage: Types, Hierarchies, and Management

Core Concepts: What is a File System?

A file system is the method and data structure that an operating system uses to control how data is stored and retrieved. It organizes data into files and directories, manages access permissions, and ensures efficient storage usage.

How File Systems Work

1. Logical Organization: Files are stored as sequences of blocks on disk, with metadata (name, size, permissions) tracked in a file allocation table (FAT) or inode table.
2. Physical Storage: Data is written to sectors (512 bytes) on disks, grouped into clusters (e.g., 4KB) for allocation.
3. Hierarchy: Uses a tree structure (root → directories → files) for navigation.

classDiagram
    class FileSystem {
        +Organizes data into files/directories
        +Manages metadata (permissions, timestamps)
        +Handles storage allocation (FAT/inode)
    }
    class StorageDevice {
        +HDD/SSD/NAS
        +Stores data in sectors/clusters
    }
    FileSystem --> StorageDevice : "Uses"

File System Types: Comparison Table

Storage Technologies: HDD vs SSD vs NAS

1. HDD (Hard Disk Drive)

• Mechanism: Magnetic platters + read/write heads.
• Speed: 50–150 MB/s (rotational latency).
• Capacity: 500GB–20TB.
• Cost: Cheaper per GB.

stateDiagram-v2
    [*] --> HDD: Spinning
    HDD --> Seek: Head moves to track
    Seek --> Read/Write: Data transfer
    Read/Write --> [*]

2. SSD (Solid State Drive)

• Mechanism: NAND flash memory (no moving parts).
• Speed: 300–3500 MB/s (no seek time).
• Capacity: 120GB–16TB.
• Cost: Expensive per GB but faster.

3. NAS (Network-Attached Storage)

• Definition: Dedicated file-level storage device on a network (e.g., Synology, QNAP).
• Use Case: Centralized storage for multiple users/devices (e.g., home media servers, backups).
• Protocols: NFS, SMB, AFP.

Partitioning and Mounting

Why Partition?

• Logical separation: Isolate OS, apps, and data.
• Performance: Different file systems for different needs (e.g., /boot on FAT32, /home on ext4).
• Security: Restrict access to sensitive partitions.

How to Partition (Linux Example)

1. Create partitions using fdisk or gparted:

   sudo fdisk /dev/sdb
   

2. Format with a file system:

   sudo mkfs.ext4 /dev/sdb1
   

3. Mount to a directory:

   sudo mount /dev/sdb1 /mnt/data
   

RAID Levels: Redundancy and Performance

RAID (Redundant Array of Independent Disks) combines multiple disks for speed, capacity, or fault tolerance.

Backup Strategies: 3-2-1 Rule

Goal: Protect against data loss (hardware failure, ransomware, human error). Rule:

• 3 copies of data.
• 2 different media (e.g., HDD + cloud).
• 1 offsite backup.

Backup Types

In the Real World

1. eSewa (Nepal):

   • Uses RAID 10 for transaction databases to ensure zero downtime during peak hours (e.g., Dashain/Tihar).
   • ext4 file system for Linux servers to handle high I/O from payment processing.

2. Ncell (Nepal):

   • Deploys SSDs in core routers to reduce latency in 4G/5G networks (critical for real-time calls/data).
   • ZFS storage for backup systems to enable instant snapshots of customer data.

3. Daraz (Alibaba Group):

   • NAS clusters store product images and inventory data across multiple regions for low-latency access.
   • RAID 5 for user uploads (photos/videos) to balance cost and redundancy.

Worked Example: Kathmandu Traffic Route Optimization

Scenario: A city’s traffic management system uses partitioned storage to log GPS data from vehicles.

• Partitioning:
  • /var/log/traffic (ext4) for real-time data.
  • /backup/traffic (RAID 1) for historical analytics.
• File System: ext4 (journaling to prevent corruption during power outages).
• Backup: Daily incremental backups to an offsite NAS.

Exam Tip

1. Diagrams: Always draw partition layouts or RAID configurations in exams (e.g., "Show RAID 5 with 4 disks").
2. Commands: Know fdisk, mkfs, mount, and rsync syntax for practical questions.
3. Comparisons: Memorize FAT32 vs NTFS vs ext4 features (e.g., "Which supports large files?").
4. Real-World Links: Connect concepts to eSewa (RAID), Ncell (SSD), or Daraz (NAS) in short-answer questions.
5. 3-2-1 Rule: Expect questions on backup strategies (e.g., "Design a backup for a hospital’s patient records").

flowchart TD
    A["File System"] --> B["FAT32<br/>NTFS<br/>ext4"]
    A --> C["Storage<br/>HDD/SSD/NAS"]
    B --> D["Partitioning"]
    C --> E["RAID<br/>0/1/5/10"]
    D --> F["Mounting<br/>/boot, /home"]
    E --> G["Backup<br/>3-2-1 Rule"]
    G --> H["Tools<br/>rsync, Borg"]