OracleExtended

Distance Clusters指的是RAC的节点分别放在不同的地方，这些节点可以放在不同的机房，也可以放在不同的城市

主要条件

距离最好小于100KM,两节点之间要有独用的光纤专线(国内有案例是租用裸光纤)

主要用途

不适合于全量灾备恢复，只适合防范停电，空难，洪水等灾难性事故

是否推荐

Oracle更推荐使用本地RAC加dataguard

官方原话如下

页

Oracle

RAC on Extended Distance Clusters

Oracle

RAC on Extended Distance Clusters is an architecture where servers in the

cluster reside in

locations

that are physically separate. Oracle RAC on Extended Distance Clusters provides

extremely

fast

recovery from a site failure and allows for all servers, in all sites, to

actively process transactions as

part

of a single database cluster. While this architecture creates great interest

and has been successfully

implemented,

it is critical to understand where this architecture best fits especially in

regards to distance,

latency,

and degree of protection it provides.

The

high impact of latency, and therefore distance, creates some practical

limitations as to where this

architecture

can be deployed. This architecture fits best where the

2 datacenters are located relatively

close (and where the extremely expensive costs of setting up direct cables with dedicated

channels between the siteshave already been taken.

Oracle

RAC on Extended Distance Clusters provides greater availability than local

Oracle RAC but it

may

not fit the full Disaster Recovery requirements of

every organization. Feasible separation is great

protection

for some disasters (local power outage, airplane crash,

server room flooding) but not all.

Disasters

such as earthquakes, hurricanes, and regional floods may affect a greater area.

One should

analyze

their situation in order to determine if both sites are likely to be affected

by the same disaster.

For

comprehensive protection against disasters including protection against

corruptions and regional

disasters,

Oracle recommends the use of Oracle Data Guard in

combination with Oracle RAC as

described in the Oracle Maximum Availability Architecture guidelines. Oracle Data Guard

also provides

additional

benefits such as support for rolling upgrades across Oracle versions.

Configuring

an extended distance cluster is more complex than configuring a local cluster.

Specific

focus

needs to go into node layout, voting disks, and data disk placement.

Implemented properly, this

architecture

can provide greater availability than a local Oracle RAC database, but should

be considered

with

Oracle’s Maximum Availability Architecture in mind.

异地RAC的架构

异地RAC的架构如下，两边都带存储，存储之间的数据是通过物理主机级别的镜像实现的，如ASM，两个存储分别做镜像,相当数据都是保存两份，如A机房的存储为1T，B机房的存储也是1T,这个时候主机同时挂载两个存储分别做镜像，相当可用空间还是1T，这样可以防止单个存储存在单点故障，中间用光纤相连

架构图如下

名字解释

：Dense Wavelength Division Multiplexing密集型光波复用,这是一项用来提高带宽的激光技术。该技术是在一根指定的光纤中，多路复用单个光纤载波的紧密光谱间距，以便利用可以达到的传输性能。这样，在给定的信息传输容量下，就可以减少所需要的光纤的总数量。