天行健，君子以自强不息

Oracle RAC team招人了。
想到Oracle最好的研发team来工作吗？
想接触最前沿的数据库和集群技术吗？
想了解Oracle database的下一代数据库(11.2 12g …)吗？
想跟Ricky做同事吗？
Wanna drink beer with Stefan Pommi on Fridays?
还犹豫啥，赶紧投简历!
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Oracle RAC Team Hiring……
在Oracle公司内部学习Oracle，学习Oracle的最佳学习环境，Oracle RAC是Oracle数据库产品中最富有发展潜力的技术和选件，Oracle RAC team招人进行中。。。如果你还不知道RAC是什么，也许可以先看看RAC的介绍或者白皮书

本次开放的职位是专门针对应届硕士毕业生（注意，是今年毕业的应届毕业生），今年7月或者年底之前毕业的均可，欢迎自荐或者推荐你的亲朋好友，工作地点在深圳，中英文简历请发送至： ricky.zhu@oracle.com （勿用163信箱发送，勿压缩，Oracle邮件系统拒收）

职责和要求如下仅供参考：(注意，是仅供参考）
Department:
Real application cluster (RAC) development.

Brief description:
responsible for implementing, maintaining, and enhancing test scripts, plan, and methodologies that ensure exhaustive testing of all assigned software areas to ensure software quality by exposing defects, and verifying resolutions. this is the golden opportunity to learn oracle within oracle, the challenging position provides training to lay the foundation of rac and database high availability. engineer will expose to latest oracle technologies on varies platforms. those experiences are extremely valuable toward the building solid foundations of rac and high availability systems for future system architecture integration and consulting work.

Detailed description:· leads the technical logistics behind installation, configuration, testing, defect tracking and reporting of all assigned projects
· projects include rac high availability and cluster ready system, oracle 11g’s plug & play features, oracle file system testing.
· oracle certification environment program
· oracle rac integration/upgrade tests among different platforms (linux, aix, hp-ux, solaris 64, and windows)
· product training and user documentation review
· oracle rac destructive and stress testingprofessional background

the candidate must either have a minimum of 2 years in the enterprise software industry or degree in computer science or related fields. prior experiences as a member of oracle dba, customer support, technical consulting, product development or qa teams are preferred.

Technical background:· proficient knowledge of unix/linux, and at least one of shell scripting languages.
· must have experiences in any one of the following platforms: linux, hp-ux, solaris 64, ibm/aix, windows.
· experience designing and executing destructive or performance tests is a plus.
· experience with software development lifecycle or software testing is a plus.
· experience with oracle rac is a plus.
· experience in clustered server environments or oracle rdbms is preferred.personal profile / skills:
· quick and willing to learn, self-motivator, attention to details and team player
· good verbal and written communication skills in english
· ability to multitask and deliver under pressure
· good academic records for entry-level position, new graduate welcome

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市面上关于Oracle RAC的书不多，关于ASM的新书更是少之又少，隆重向大家推荐一本ASM的新书。

Oracle Automatic Storage Management
Under-the-Hood & Practical Deployment Guide

作者是Oracle公司RAC部门的几位数据库专家。Rich Long更是ASM的开发总监。
下面是本书的简单介绍:

http://www.mhprofessional.com/product.php?isbn=0071496076

Streamline data management and provisioning using Oracle Automatic Storage Management (Oracle ASM) and the detailed information contained in this exclusive Oracle Press resource. Written by a team of database experts, Oracle Automatic Storage Management: Under-the-Hood & Practical Deployment Guide explains how to build and maintain a dynamic, highly available Oracle database storage environment. Inside, you’ll learn how to configure storage for Oracle ASM, build disk groups, use data striping and mirroring, and optimize performance. You’ll also learn how to ensure consistency across server and storage platforms, maximize data redundancy, and administer Oracle ASM from the command line.

* Manage Oracle ASM Instances and configure Oracle RDBMS instances to leverage Oracle ASM
* Define, discover, and manage disk storage under Oracle ASM
* Create external, normal-redundancy, and high-redundancy disk groups
* Add and remove Oracle ASM storage without affecting RDMS instance availability
* Learn how Oracle ASM provides even I/O distribution
* Work with Oracle ASM directories, files, templates, and aliases
* Improve storage performance and integrity using the ASMLIB API
* Simplify system administration with the Oracle ASM command line interface
* Understand key internal Oracle ASM structures and algorithms

作者简介：
Nitin Vengurlekar works at Oracle in the Real Application Cluster (RAC) engineering group, with specific emphasis on ASM. Nitin is a popular conference presenter on this topic.
Murali Vallath is an Oracle Certified Database Administrator and is president of the Oracle RAC Special Interest Group.
Rich Long is Director of Development for Automatic Storage Management at Oracle and has managed ASM development since the project’s inception.

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摘自于维基百科

High-availability cluster
From Wikipedia, the free encyclopedia

High-availability clusters (also known as HA Clusters or Failover Clusters) are computer clusters that are implemented primarily for the purpose of improving the availability of services which the cluster provides. They operate by having redundant computers or nodes which are then used to provide service when system components fail. Normally, if a server with a particular application crashes, the application will be unavailable until someone fixes the crashed server. HA clustering remedies this situation by detecting hardware/software faults, and immediately restarting the application on another system without requiring administrative intervention, a process known as Failover. As part of this process, clustering software may configure the node before starting the application on it. For example, appropriate filesystems may need to be imported and mounted, network hardware may have to be configured, and some supporting applications may need to be running as well.

HA clusters are often used for critical databases, file sharing on a network, business applications, and customer services such as electronic commerce websites.

HA cluster implementations attempt to build redundancy into a cluster to eliminate single points of failure, including multiple network connections and data storage which is multiply connected via Storage area networks.

HA clusters usually use a heartbeat private network connection which is used to monitor the health and status of each node in the cluster. One subtle, but serious condition every clustering software must be able to handle is split-brain. Split-brain occurs when all of the private links go down simultaneously, but the cluster nodes are still running. If that happens, each node in the cluster may mistakenly decide that every other node has gone down and attempt to start services that other nodes are still running. Having duplicate instances of services may cause data corruption on the shared storage.
Node configurations

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之前好几个同事聊天的时候，说想自己装个RAC玩玩，怎么的也得两个节点吧，不行就整个虚拟机。VM team的同事干脆就用Oracle VM了。其实个人玩RAC也不是不可能，只要解决几个关键的问题就行了，比如双网卡，共享设备等。其中最关键的就是共享设备了，在一个独立硬盘上创建裸设备，作为OCR和Voting DISK甚至ASM的磁盘，下面就介绍一下，在Linux下面如何创建裸设备，也就是create raw device. 大致这么几个步骤：

1. Check iscsi has been autoenable;
using “/sbin/chkconfig –list|grep iscsi”. If it is enabled, using “/sbin/chkconfig –level 2345 iscsi on” to enable it.
2. using “fdisk -l ” to check the partition information;
“/sbin/fdisk -l /dev/sde”, and then use “fdisk” to create new partitions
3. Create “/etc/udev/devices/raw” directory if it does not exist;
4. Create “/dev/raw” directory if it does not exist;
5. Create new raw device on each node, using:
“mknod /etc/udev/devices/raw/name c 162 2″
And then change the device permissions;
6. Edit “/etc/sysconfig/rawdevices” to add new items referring to new partitions on each node; such as “/etc/udev/devices/raw/name /dev/b_name”;
7. run “/sbin/udevstart” and check whether new raw devices have been generate in “/etc/udev/devices/raw” and “/dev/raw/”;
8. Changt the mode and own of the raw devices under “/dev/” directory;
9. service rawdevices restart

至此，就基本可以了，注意OCR和VD只能建在raw device上。
多谢blue_prince指正：其实OCR和VOTING DISK不一定非要在祼设备上面不可，以OCFS或者共享的NFS上面也可以的，只是可靠性不如祼设备那么强而已

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众所周知，在安装Oracle Clusterware（Former Oracle CRS）之前，有一些必备的条件，比如双网卡，同版本的操作系统，一些必需的补丁等等，还有一些比如同样ID的组和用户，这些都可以通过clusterware附带的一个检查工具cluvfy进行检查。详细的列表和检查方法可以参考oracle的官方安装文档
除此之外，安装之前另外一个重要的前提就是ssh或者rsh的配置，这就是oracle在节点之间进行文件copy时候必须的，下面就分十个步骤介绍如何进行ssh的配置。

1. Login as oracle user
2. create .ssh directory in the oracle user’s home directory
$cd
$mkdir ~/.ssh
$chmod 700 ~/.ssh

3. Generate an RSA and DSA key for SSH
$/usr/bin/ssh-keygen -t rsa
$/usr/bin/ssh-keygen -t dsa

4. After this, four files generated
~/.ssh/id_rsa.pub
~/.ssh/id_rsa
~/.ssh/id_dsa.pub
~/.ssh/id_dsa

5. Create an authorized key file
$touch ~/.ssh/authorized_keys
$cd ~/.ssh
$ls

6. Copy the contents of rsa.pub and dsa.pub files to authrorized file
[oracle@node1 .ssh]$ ssh node1 cat /home/oracle/.ssh/id_rsa.pub >> authorized_keys
oracle@node1’s password:
[oracle@node1 .ssh]$ ssh node1 cat /home/oracle/.ssh/id_dsa.pub >> authorized_keys
[oracle@node1 .ssh$ ssh node2 cat /home/oracle/.ssh/id_rsa.pub >> authorized_keys
oracle@node2’s password:
[oracle@node1 .ssh$ ssh node2 cat /home/oracle/.ssh/id_dsa.pub >>authorized_keys
oracle@node2’s password:

7. Use scp to copy the authorized file to other nodes in ~/.ssh
[oracle@node1 .ssh]scp authorized_keys node2:/home/oracle/.ssh/

8. Change the permissions on the oracle user’s authorized file on all cluster nodes
$ chmod 600 ~/.ssh/authorized_keys

9. Enable OUI to use ssh and scp
$ exec /usr/bin/ssh-agent $SHELL
$ /usr/bin/ssh-add

10. Verify ssh configuration on all nodes
$ ssh nodename1 date
$ ssh nodename2 date

其他的具体步骤可以参考oracle的手册B28264-03，地址如下：
http://download.oracle.com/docs/cd/B28359_01/install.111/b28264/toc.htm

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如何更好的理解SunCluster的Quorum，也就是选举盘，下面就结合例子做介绍。
其实说到底就是两个公式：

一个是计算选举盘是否足够的公式：
Q=TCV/2+1
TCV就是当前cluster中配置的总票数，Toally configured Votes.
至于如何计算总票数，就是第二个公式了：
TCV=node 票数+device 票数
node票数很容易计算，每个节点一票
device票数计算方法是：
QD=TCD-1
TCD就是连接当前共享设备的所有的节点数-1

下面是详细的说明：
To form a cluster and offer services, the nodes in a cluster must first reach quorum. The quorum equation states that a cluster must have the total number of configured votes, divided by two (remainders are discarded), plus one (Q = TCV/2 + 1). If a cluster cannot reach quorum, then it does not form. The individual cluster nodes do not boot fully, but wait until enough votes are available to reach quorum. If a running cluster loses quorum, the affected nodes panic and try to reboot (assuming auto-boot? is set to true on those nodes). Machines can be booted outside the cluster by issuing a boot -x from the OBP, but no cluster services will be available on these machines.

The key to understanding quorum is learning how votes are assigned and counted. Each node in a configured cluster has one (1) quorum vote. Each shared storage device configured as a quorum device has votes totaling the number of connected devices minus one (QD = TCD - 1). Ownership of a quorum device is assigned to one controlling node based on SCSI reservations.
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因为测试需要，我会比较频繁的安装和卸载Oracle Clusterware，RAC，卸载和安装本身都有OUI工具可以使用，但是速度比较慢，而且需要过多的人工干预。如果直接把OracleHome删掉，杀掉所有相关进程，重启机器也可以解决问题，不过我认为这是一种比较粗暴的方式。
如果采用自动化的手段不仅可以提高效率，而且对于了解卸载本身的过程有一定帮助，今天就结合我写的一个简单的脚本介绍一下如何用六步快速安全卸载Oracle RAC。

脚本分为这么几个部分：
1. stop and delete RAC instance, drop the database
2. stop and delete ASM instance
3. stop and delete listener
4. stop crs stack and clean related resource
5. clean ocr context
6. change permission and remove related ORACLE directory and Clusterware directory

其中4，5都可以直接利用Clusterware 目录install下面的脚本进行，所以这里主要介绍1，2，3，6.
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