Oracle: ASM disk

Every ASM disk is divided into allocation units (AU).

The AU is the fundamental allocation unit on an ASM disk.

A file extent consists of one or more AUs, a file consists of one or more file extents.

The size of the disk's AUs are set with the disk group attribute AU_SIZE. Possible values are 1, 2, 4, 8, 16, 32 or 64 MB.

Data warehouses and OLAP environments tend to have larger AUs because they have large sequential reads.