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Data on External Storage in DBMS



The storage system in a DBMS refers to the hierarchical arrangement of storage devices and media to store, manage, and retrieve data efficiently. The system is designed to handle different storage capacities, access speeds, volatility, and costs.

Storage System Hierarchy in DBMS

The storage hierarchy typically has multiple levels, each with its specific characteristics. Here's a typical hierarchy from fastest (and usually most expensive per byte) to slowest (and usually least expensive per byte):

1. Registers

  • Located within the CPU.
  • Smallest and fastest type of storage.
  • Used to hold data currently being processed.

2. Cache Memory (L1, L2, L3 caches)

  • On or very close to the CPU.
  • Extremely fast but small in size.
  • Acts as a buffer for frequently used data.

3. Main Memory (RAM)

  • Data that's actively being used or processed is loaded here.
  • Faster than secondary storage.
  • Volatile in nature (i.e., data is lost when power is turned off).

4. Flash Storage (Solid State Drives - SSD)

  • No moving parts.
  • Faster than traditional hard drives.
  • More durable and reliable.

5. Magnetic Disks (Hard Disk Drives - HDD)

  • Primary secondary storage medium.
  • Non-volatile, persistent storage.
  • Data is stored in tracks, sectors, and cylinders.
  • Slower than main memory but offers a large storage capacity at a lower cost.

6. Optical Disks (CD, DVD, Blu-Ray)

  • Data is read using lasers.
  • Slower than magnetic disks and usually have less storage capacity.
  • Portable and commonly used for media and software distribution.

7. Magnetic Tapes

  • Sequential access storage, unlike disks which are random access.
  • Often used for backups and archiving due to their high capacity and low cost.
  • Much slower access times compared to magnetic disks.

8. Remote Storage/Cloud Storage

  • Data stored in remote servers and accessed over the internet.
  • Provides scalability, availability, and fault-tolerance.
  • Latency depends on network speed and distance to servers.

Types of Storage:

  1. Primary Storage: Includes registers, cache memory, and main memory (RAM). It's the main memory where the operating system, application programs, and data in current use are kept for quick access by the computer's processor.
  2. Secondary Storage: Encompasses data storage devices like HDDs, SSDs, CDs, and USB drives. It is non-volatile and retains data even when the computer is turned off.
  3. Tertiary Storage or Off-line Storage: Often involves magnetic tape systems or optical disk archives. This is slower than secondary storage and is used for data archiving and backup.
  4. Quaternary Storage: Refers to methods like cloud storage or other remote storage techniques where data is stored in remote servers and is fetched over the internet or other networks.

Note: The storage hierarchy in a DBMS serves as a framework for balancing the trade-offs between cost, speed, and capacity. By strategically using different levels of this hierarchy, a DBMS can ensure fast access times for frequently used data while also providing large-capacity storage for data that's accessed less frequently.

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