Oracle OCP 1Z0-053 Q115(ASM variable extent size support)

115.What are the advantages of variable extent size support for large ASM files? (Choose two.)
A. It improves resync operations when the disk comes online after being taken offline for maintenance
purposes.
B. It improves performance in the extended cluster configuration by reading from a local copy of an
extent.
C. Fewer extent pointers are needed to describe the file and less memory is required to manage the
extent maps in the shared pool.
D. This feature enables faster file opens because of the reduction in the amount of memory that is
required to store file extents.
Answer: CD

參考：http://blog.csdn.net/rlhua/article/details/14388387

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.

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