OCP-1Z0-053-V12.02-115题

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
答案解析：
参考：http://docs.oracle.com/cd/E11882_01/server.112/e18951/asmcon.htm#OSTMG94064

C.只需要较少的区指针就可以描述文件以及只需要较少的内存去管理在共享池中的区映像。

D.此功能可以更快地打开文件，因为需要存储文件区的内存量减少。

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 to 11.1 or higher.

The extent size of a file varies as follows:

Extent size always equals the disk group AU size for the first 20000 extent sets (0 - 19999).

Extent size equals 4*AU size for the next 20000 extent sets (20000 - 39999).

Extent size equals 16*AU size for the next 20000 and higher extent sets (40000+).