DB C7 Storage and File Structure

RECALL Storage Manager:

ref Database System Concepts and Design P560.

Overview of Physical Storage Media

Classification

• By Speed and Cost:

  • cache: Fastest and mostly costly, volatile, managed by computer system and hardware.

  • Main-Memory: Fast, volatile, generally too small to store the entire DB.

  • Flash Memory: Non-vlatile, support read(fast), write(slow) and erase(slower).

    Solid-state drive, SSD: uses flash memory internally to store data but provides an interface similar to a magnetic disk, allowing data to be stored or retrieved in units of a block; such an interface is called a block-oriented interface.

  • Magnetic-disk: primary medium for the long-term online storage of data, aslo called hard disk drive (HDD). The system must first move the data from disk to main memory to access disk data; the data modified must be written to disk after the designated operations.

  • Optical / Tape storage: Old.

• By Reliability:

  • volatile storage: Data loss on power failure or system crash. e.g DDR2,SQR
  • Non-volatile storage: contents persists even the power is switched off.

Magnetic-disk

Physical Characteristics of Disks

Each disk platter has a flat, circular shape.

• Its two surfaces are covered with a magnetic material, and information is recorded on the surfaces.
• Platters are made from rigid metal or glass.

tracks and sectors: The disk surface is logically divided into tracks. Tracks are subdivided into sectors.

• A sector is the smallest unit of information that can be read from or written to the disk.
• Sector sizes are typically 512 bytes.
• The inner tracks (closer to the spindle) are of smaller length than the outer tracks;The outer tracks contain more sectors than the inner track.

read–write head:

Disk subsystem

Performance measure