天行健，君子以自强不息

最近试用了一下OCFS2，这是一个全新的集群文件系统，有自己的节点管理，心跳等集群中的概念，而且相对OCFS来说，有很大的改进，是一个全新的文件系统，支持较多的Oracle文件，包括OCR和Voting Disk等。
但是和ASM和RAW比起来，还是有一些本质的不同，在网上看到关于这几者之间的一个大讨论，特别深入，转载一下，学习之。 原文地址：http://zhouwf0726.itpub.net/post/9689/221194

先看一下Oracle OCFS2的官方定义：
WHAT IS OCFS2?

OCFS2 is the next generation of the Oracle Cluster File System for Linux. It is an extent based, POSIX compliant file system. Unlike the previous release (OCFS), OCFS2 is a general-purpose file system that can be used for shared Oracle home installations making management of Oracle Real Application Cluster (RAC) installations even easier. Among the new features and benefits are:

* Node and architecture local files using Context Dependent Symbolic Links (CDSL)
* Network based pluggable DLM
* Improved journaling / node recovery using the Linux Kernel “JBD” subsystem
* Improved performance of meta-data operations (space allocation, locking, etc).
* Improved data caching / locking (for files such as oracle binaries, libraries, etc)

这个大讨论是从一个问题引起的：200亿条数据，就是20T吧，用ASM好？还是用OCFS好？还是用RAW好？
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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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周日从深圳图书馆淘的一本《使用SAN与NAS》，现在做做读书笔记。

SAN的概念定义：SAN就是两个或者多个设备通过串行SCSI协议进行通信，比如Fibre Channel或者iSCSI。

NAS的概念定义：NAS（网络附属存储）是指通过NFS，CIFS或者DAFS共享文件的计算机（或者设备）。

对比如下：

SAN:
协议: 串行SCSI-3
共享: 原始磁盘或者磁带
允许: 不同的服务器可以访问同一个原始磁盘或者磁带
替代: 替代本地附属磁盘

NAS:
协议: NFS/CIFS
共享: 文件系统
允许: 不同的用户可以访问同一个文件-
替代: 替代NFS/CIFS

先记录这么点，有空再写。

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最近一直在Solaris平台上，所以对Solaris平台的关注可能更多一些，前阵子测试的时候，总遇到Swap 空间不够的情况，所以对swap需要进行一些关注，现转载一篇Solaris平台Swap空间的文章。

本文介绍了在Solaris平台上Swap(交换)空间的基本概念、实现的原理以及对Swap(交换)空间进行监控的方法和调整的策略。
　　什么是SWAP(交换)空间
　　对于一般的Solaris系统管理员来说，很少会接触Swap(交换)空间，在他们看来Swap区只不过是磁盘上的一两个分区或是几个Swap(交换)文件，当系统没有足够的物理内存来处理当前进程的时候，就利用Swap(交换)空间作为虚拟内存的临时存储空间，这种说法从技术角度来说是没有错的，但 Solaris在实现Swap时有其非常独特的地方。
　　SWAP空间作用
　　众所周知，现代操作系统都实现了“虚拟内存”这一技术，不但在功能上突破了物理内存的限制，使程序可以操纵大于实际物理内存的空间，更重要的是“虚拟内存”是隔离每个进程的安全保护网，使每个进程不受其他程序的干扰。
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RAID 4: Independent Data disks with shared Parity disk

Characteristics/Advantages

1. Very high Read data transaction rate

2. Low ratio of ECC (Parity) disks to data disks means high efficiency

3. High aggregate Read transfer rate

Disadvantages

1. Quite complex controller design

2. Worst Write transaction rate and Write aggregate transfer rate

3. Difficult and inefficient data rebuild in the event of disk failure

4. Block Read transfer rate equal to that of a single disk

Each entire block is written onto a data disk. Parity for same rank blocks is generated on Writes, recorded on the parity disk and checked on Reads.

RAID Level 4 requires a minimum of 3 drives to implement

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RAID 3: Parallel transfer with parity

Characteristics/Advantages

1. Very high Read data transfer rate

2. Very high Write data transfer rate

3. Disk failure has an insignificant impact on throughput

4. Low ratio of ECC (Parity) disks to data disks means high efficiency

Disadvantages

1. Transaction rate equal to that of a single disk drive at best (if spindles are synchronized)

2. Controller design is fairly complex

3. Very difficult and resource intensive to do as a “software” RAID

Recommended Applications

1. Video Production and live streaming

2. Image Editing

3. Video Editing

4. Prepress Applications

5. Any application requiring high throughput

The data block is subdivided (”striped”) and written on the data disks. Stripe parity is generated on Writes, recorded on the parity disk and checked on Reads.

RAID Level 3 requires a minimum of 3 drives to implement

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RAID 2: Hamming Code ECC

Characteristics/Advantages

1. “On the fly” data error correction

2. Extremely high data transfer rates possible

3. The higher the data transfer rate required, the better the ratio of data disks to ECC disks

4. Relatively simple controller design compared to RAID levels 3,4 & 5

Disadvantages

1. Very high ratio of ECC disks to data disks with smaller word sizes - inefficient

2. Entry level cost very high - requires very high transfer rate requirement to justify

3. Transaction rate is equal to that of a single disk at best (with spindle synchronization)

4. No commercial implementations exist / not commercially viable

Each bit of data word is written to a data disk drive (4 in this example: 0 to 3). Each data word has its Hamming Code ECC word recorded on the ECC disks. On Read, the ECC code verifies correct data or corrects single disk errors.

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RAID1: Mirroring and Duplexing

Characteristics/Advantages

1. One Write or two Reads possible per mirrored pair

2. Twice the Read transaction rate of single disks, same Write transaction rate as single disks

3. 100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk

4. Transfer rate per block is equal to that of a single disk

5. Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures

6. Simplest RAID storage subsystem design

Disadvantages

1. Highest disk overhead of all RAID types (100%) - inefficient

2. Typically the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended

3. May not support hot swap of failed disk when implemented in “software”

Recommended Applications

1. Accounting

2. Payroll

3. Financial

4. Any application requiring very high availability

For Highest performance, the controller must be able to perform two concurrent separate Reads per mirrored pair or two duplicate Writes per mirrored pair.

RAID Level 1 requires a minimum of 2 drives to implement

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