oracle asm 磁盘管理什么场景该用什么样的冗余方式

oracle asm 创建磁盘组的时候，有三种冗余方式，
第一：外部冗余方式，依赖于存储的镜像
第二：正常冗余方式，asm存储镜像双份镜像方式
第三：高度冗余方式，asm存储镜像三份镜像方式

Mirroring Options for ASM Disk Group Types
Disk Group Type Supported Mirroring Levels Default Mirroring Level
External redundancy Unprotected (none) Unprotected

Normal redundancy Two-way
Three-way
Unprotected (None) Two-way

High redundancy Three-way Three-way

那什么场景下该用哪种冗余方式呢，以下是官方文档介绍

When Should External, Normal, or High Redundancy Be Used?
ASM mirroring runs on the database server and Oracle recommends to off load this
processing to the storage hardware RAID controller by using external redundancy. You
can use normal redundancy in the following scenarios:
■ Storage system does not have RAID controller
■ Mirroring across storage arrays
■ Extended cluster configurations
In general, ASM mirroring is the Oracle alternative to third party logical volume
managers. ASM mirroring eliminates the need to deploy additional layers of software
complexity in your Oracle database environment.

外部冗余方式通常用于存储上已经做好raid的镜像方式

正常冗余和高度冗余用于存储上没有做raid镜像方式，跨存储阵列的镜像，比如双盘柜，还有扩展集群配置等。