Creating Chunk Files on UNIX

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Creating Chunk Files on UNIX

On UNIX, you can store data in chunks that use either unbuffered (raw) disks or operating-system files, also known as buffered or cooked files.

Raw or Unbuffered Disk Access

UNIX provides unbuffered disk access using character-special devices (also known as raw disk devices). To create raw disk devices on UNIX, follow the instructions provided with your operating system.

The database server uses raw disk access to improve the speed and reliability of disk I/O operations. Raw disk access bypasses the file-buffering mechanism that the operating system provides. The database server itself manages the data transfers between disk and memory. The database server optimizes table access by guaranteeing that rows are stored contiguously.

Important:

While you should use raw disk devices on UNIX to achieve better performance, recent advances in I/O caching for cooked writes can provide similar if not better performance. To determine the best device performance, perform benchmark testing on the system with both types of devices for the dbspace and table layout.

To allocate disks for the database server

Configure a raw disk device for each disk.
Create standard device names or filenames.
Set permissions, ownership, and group for each raw disk device.

Cooked Files

If optimum performance is unimportant, you can configure the database server to store data in cooked files. Cooked files are easier to set up than raw disk devices.