Parallel Disks (Cont.), File Systems

Database Systems - CS2300 - 1 February 2018

RAID Table

I/O

  • Block: A unit of information communicated between disk and I/O buffer
  • Access Time: Seek time + rotational time (latency) + transfer rate

Buffers are used to make I/O operations happen without hitching the CPU.

The CPU buffers all transactions to the I/O in a technique called double buffering

Files, File Systems

  • A file is a collection of records of the same record type (same format and definition)
  • A record is a collection of fields. It represents a collection of related data values identifying an entity. Each field then represents an attribute of an entity.
Vocab:
  • File is a relation
  • Record is a tuple
  • Field is an attribute
  • Data type is the domain of each attribute

File types

  • Files can have either a fixed length record, or a variable length record