Chapter 8: Data Storage Design and SQL Server

Posted by Apress Free Book | ADO.NET & Database December 16, 2008
This chapter will explore the most common storage technologies available to you. It will also present some benefits and concerns about different storage designs so that you can more easily choose what suits your solution. We will finish the chapter with a presentation of SQL Server-examining its architecture and how it fits into your storage policy.

ALL APPLICATIONS YOU BUILD store data in some way or another. It has become vital for enterprises to increase efficiency and reduce Total Cost of Ownership (TCO) for data storage as well as all other infrastructure components.
Many factors must be considered when planning storage: Do you need data to be available 24 hours a day? What recovery times can you accept if data is compromised in any way? How much will your data grow with time? Are you using your data storage architecture effectively as it is ? 
It is not only your applications that need to be designed carefully. When it comes to storing data, you need to weigh an increasing number of issues, not only for the application you are currently building, but also for the entire enterprise data storage design. Considering how much important data is actually stored at a given company, it is surprising that many do not take it as seriously as they should.
Many enterprises create new database servers for almost every new application. This has resulted in data being scattered all over such companies and storage areas not being fully utilized. The scattered data has made manageability harder and more costly than it should be. By not using data storage effectively, a lot of investment is wasted, costing money in the long run. 
Availability, scalability, and security have been emphasized throughout this book. These topics are important not only when building applications, but also when it comes to designing storage architecture. You can use various technologies to increase these aspects of an application, but they have some trade-offs that you need to consider. Availability always costs money. Redundant technology comes with a rather hefty price tag, and this is true in development and in data storage alike. When you try to increase scalability, availability can suffer. This requires you to purchase even more hardware to avoid problems. 
Security most often affects performance and manageability due to the added overhead and complexity of secure solutions. The more you tighten security, the more performance and manageability suffers as a direct result. 
You need to design your storage solution to meet goals of lowered TCO, high availability, great scalability, tight security, and, of course, simplified management. That is quite a lot to live up to, as you can see. When you design your storage solution, you must plan for enabling your organization to quickly create new business applications, and at the same time provide security and minimize the potential of data loss. You must also make sure new applications can be implemented with minimum disruption to your existing business. The decisions you make for the data storage architecture have an impact on how you design your future business
The tasks facing a data storage team are not easy ones, so first we will take a look at some of the technologies for storing data and see how they can ease the burden. Then we will move on to choosing and implementing a logical design for a storage system before diving into SQL Server. 
This chapter will explore the most common storage technologies available to you. It will also present some benefits and concerns about different storage designs so that you can more easily choose what suits your solution. We will finish the chapter with a presentation of SQL Server-examining its architecture and how it fits into your storage policy.
Three Storage Technologies
There are basically three different storage technologies you can use: Storage Area Networks (SANs), network-attached storage (NAS), and direct-attached storage (DAS). They each have their advantages and disadvantages, naturally; but by combining them, you can perhaps overcome their individual shortcomings. We will look at these in more detail in the following sections.
Storage Area Networks (SANs)

A SAN is a specialized network, the sole purpose of which is to provide access to high performance and highly available storage subsystems. This solution is quite interesting. The SAN is constructed of several devices, all interconnected by fiber or copper wiring. The subsystem is available to multiple applications at the same time, just like a network-attached storage appliance. The major difference is that it provides higher scalability and performance. Even though a DAS is still faster than a SAN, this performance gap is diminishing constantly with the evolution of SAN technology. (For more on DAS, see the section "Direct-Attached Storage.") 
The SAN concept is quite simple. An external RAID (short for redundant array of independent disks, sometimes called redundant array of inexpensive disks) cabinet has a connection directly from the Host Bus Adapter (HBA) to the external RAID subsystem. The SAN, on the other hand, connects the HBA to a switch instead, providing other servers access to the data storage that way (see Figure 8-1).
  Figure 8-1. A SAN connects the HBA to a switch.
Next we will take a closer look at NAS and DAS, after which we will introduce you to the logical designs of storage solutions.
Network-Attached Storage (NAS)
A network-attached storage system is a file server, to put it simply. This solution is built on an operating system, often designed for the sole purpose of providing file services. It thereby provides a flexible and scalable solution for most enterprises. Many applications can access a NAS appliance over the LAN by using protocols like TCP/IP. Since this solution is accessed across a LAN, performance might be slow. When compared to a DAS system, performance is lower, but with the help of Gigabit Ethernet you can decrease this performance hit.
Windows Storage Server 2003

Microsoft has developed a dedicated file server based on Windows Server 2003. This edition of the Windows Server family is called Windows Storage Server 2003 and is only available through OEMs. The Storage Server is enhanced to offer a scalable, available, quickly recoverable solution for enterprise file servers. Besides being a file server, the Windows Storage Server 2003 also acts as a gateway to SANs, so you are not limited to the features offered in the server itself. To learn more about this server, direct your Web browser to
Direct-Attached Storage (DAS)

As the name implies, direct-attached storage refers to a storage device directly attached to a server, specifically local hard drives and RAID systems attached with an IDE or SCSI interface to a computer. 
This solution is fast and allows great performance on the server it is attached to, and often only the attached server can access it. This could be a great solution for a small SQL Server perhaps, but if you are planning a larger enterprise application with clustering, this is not a good choice, because many servers might need to access it to provide redundancy.

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