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Oracle OCP 1Z0-050（27题）解析

QUESTION 27:

What is the advantage of setting the ASM-preferred mirror read for the Stretch cluster configuration?

题目大意是：设置ASM首选的镜像读（充分利用cluster配置）的优势是什么？

A. It improves performance by reading from a copy of an extent closest to the node.

B. This feature enables much faster file opens.

C. It improves performance as fewer extent pointers are needed in the shared pool.

D. It improves resync operations.

Answer: A

解析：

参考Oracle官方文档：

Oracle ASM Preferred Read Disk Groups

In previous releases, Oracle ASM used the disk with the primary copy of a mirrored extent as the preferred disk for data read operations. With this release, using the new initialization file parameter asm_preferred_read_failure_groups, you can specify disks located near a specific cluster node as the preferred disks from which that node obtains mirrored data. This option is presented in DBCA, or you can configure it after installation. This change facilitates faster processing of data with widely distributed shared storage systems or with extended clusters (clusters whose nodes are geographically dispersed), and improves disaster recovery preparedness.

When you configure Oracle ASM failure groups, it may be more efficient for a node to read from an extent that is closest to the node, even if that extent is a secondary extent. You can configure Oracle ASM to read from a secondary extent if that extent is closer to the node instead of Oracle ASM reading from the primary copy which might be farther from the node. Using preferred read failure groups is most beneficial in an extended distance cluster.

To configure this feature, set the ASM_PREFERRED_READ_FAILURE_GROUPS initialization parameter to specify a list of failure group names as preferred read disks. Oracle recommends that you configure at least one mirrored extent copy from a disk that is local to a node in an extended cluster. However, a failure group that is preferred for one instance might be remote to another instance in the same Oracle RAC database. The parameter setting for preferred read failure groups is instance specific.

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