COSI 127b Lecture Notes - Lecture 5: Third Normal Form, Hard Disk Drive Performance Characteristics, Standard Raid Levels

• School: Brandeis University
• Department: Computer Science
• Course: COSI 127b
• Professor: Cherniack

Document Summary

Primary storage (cache and main memory) is volatile. Secondary (flash memory and disk) and tertiary (tape) storage is non volatile. Primary storage is faster, but secondary storage is cheaper. A block is the smallest unit of addressable disk memory. The main concerns for data transfers between memory and disk are efficiency/speed and safety/reliability. Efficiency can be achieved by improving raw data transfer speed via fast disks and parallelization, avoiding untimely data transfers via disk scheduling and batching, and avoiding unnecessary data transfers via buffer management and good file organization. Disk speed is measured by seek time (the time to get to the location), latency time (the time spent waiting at the location), and data transfer time (the time spent moving data from disk to buffer). Seek time and latency time comprise access time. It is cheaper to have many small disks instead of a few large disks. Data can be distributed as entire files or in parts (striping).