11gOCP精解 之 04

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You are managing an Oracle Database 11g ASM instance having three disks in a disk group with compatibility attribute set to 11.1.0 and set to high. One of the disks in the disk group becomes unavailable because of power failure. Which statements will be true in this scenario? (Choose all that apply.)

 

A. The disk is immediately dropped from the disk group.

B.The ASM tracks the extents that

C. The ASM migrates the extents from the unavailable disk to the remaining disks.

D. The disk automatically goes offline.

Answer: B,D

Explanation:

 

Disks

磁碟組建立時使用CREATE DISKGROUP 語句， 建立時允許我們設定冗餘項：

 

   NORMAL REDUNDANCY - Two-way mirroring, requiring two failure groups.

   HIGH REDUNDANCY - Three-way mirroring, requiring three failure groups.

   EXTERNAL REDUNDANCY - No mirroring for disks that are already protected using hardware mirroring or RAID. If you have hardware RAID it should be used in preference to ASM redundancy, so this will be the standard option for most installations.

 

在短暫的磁碟故障發生時,  ASM 保持跟蹤記錄那些要被寫入掉線的磁碟中所改變的部分； 一旦磁碟再次可以使用時，那些改變的部分變被再次的同步到磁碟中， 而不是被覆寫全盤的內容；這種機制可以適當的加快重新同步資料的效率；

快速映象同步（fast mirror resync） 這種機制僅僅在磁碟組的 compatibility attributes 被設定為 11.1 or higher才生效

 

How ASM Manages Disk Failures

取決於磁碟組的冗餘級別和定義的故障組，一個或多個的故障磁碟可能導致以下結果之一:

1.首先磁碟被下線隨後被自動的下線；在這種情況下磁碟組一直掛載著並且提供著服務；另外由於映象的存在，所有的磁碟組的資訊保持健康的狀態；隨後在磁碟移除的操作之後，ASM執行一個再平衡調整用於重建全部的冗餘項來恢復那些在壞掉的磁碟的上的資料

2.全部的磁碟組自動的解除安裝，這意味著丟失掉的資料的可訪問性

所以選擇B，D