OCP 1Z0 053 129

129.You are managing an Oracle Database 11g database with ASM storage. The ASM disk group has the 
COMPATIBLE.ASM attribute set to 11.1. Which statements are true regarding extent management and 
allocation units in the ASM disk group? (Choose all that apply.) 
A. The au_size disk group attribute determines the size of allocation units in the disk group. 
B. The allocation unit size may vary but the extent size is fixed. 
C. The allocation unit size and extent size are fixed for all the disks in a disk group and cannot be 
changed.
D. Extent management is completely automated.
Answer: AD

http://docs.oracle.com/cd/E11882_01/server.112/e18951/asmcon.htm#BABCIIAA

Allocation Units

Every Oracle ASM disk is divided into allocation units (AU). An allocation unit is thefundamental unit of allocation within a disk group. A file extent consists of one or more allocation units. An Oracle ASM file consists of one or more file extents.

When you create a disk group, you can set the Oracle ASM allocation unit size with the AU_SIZE disk group attribute. The values can be 1, 2, 4, 8, 16, 32, or 64 MB, depending on the specific disk group compatibility level. Larger AU sizes typically provide performance advantages for data warehouse applications that use large sequential reads.

http://docs.oracle.com/cd/E11882_01/server.112/e18951/asmcon.htm#BABDEIJI

Extents

The contents of Oracle ASM files are stored in a disk group as a set, or collection, of extents that are stored on individual disks within disk groups. Each extent resides on an individual disk. Extents consist of one or more allocation units (AU). To accommodate increasingly larger files, Oracle ASM uses variable size extents.

Variable size extents enable support for larger Oracle ASM data files, reduce SGA memory requirements for very large databases, and improve performance for file create and open operations. The initial extent size equals the disk group allocation unit size and it increases by a factor of 4 or 16 at predefined thresholds. This feature is automatic for newly created and resized data files when specific disk group compatibility attributes are set to11.1 or higher.