Offsets

The system administrator might divide a physical disk into partitions, which are different parts of a disk that have separate pathnames. Although you should use an entire disk partition when you allocate a chunk on a raw disk device, you can subdivide partitions or cooked files into smaller chunks using offsets. For more information, see Disk-Layout Guidelines.

An offset allows you to indicate the location of a given chunk on the disk partition, file, or device. For example, suppose that you create a 1000-kilobyte chunk that you want to divide into two chunks of 500 kilobytes each. You can use an offset of zero kilobytes to mark the beginning of the first chunk and an offset of 500 kilobytes to mark the beginning of the second chunk.

You can specify an offset whenever you create, add, or drop a chunk from a dbspace, blobspace, or sbspace.

You might also need to specify an offset to prevent the database server from overwriting partition information. Allocating Raw Disk Space on UNIX explains when and how to specify an offset.