Disks are the heart and soul of a database system ”they physically store the data accessed by the database server. From both performance and high availability standpoints, ensuring a proper disk configuration is one of, if not the most, important aspect of planning and configuration when it comes to the system that will run Microsoft SQL Server 2000. Even though the decisions of how many processors and how much memory you need are important, you will probably get the most from your SQL Server investment by planning and implementing the best disk subsystem for your needs.
Whenever you design a system for availability, growth, and performance, as noted in Chapter 1, Preparing for High Availability, there is some form of trade- off involved. This chapter guides you step by step through the decision-making, planning, and implementation of disk subsystems used with SQL Server.
This section defines a few terms that are used throughout the rest of the chapter.
Spindle The physical disk itself. The term is derived from the shape of the disk inside the enclosure, which is a round platter with a head, somewhat resembling a spindle.
Logical Unit, LUN This will be hardware and software vendor “ dependent, but each of these terms has the same meaning ”it is one physical disk or a group of disks that appear as one unit to the operating system at a physical level.
If you want to configure more than eight LUNs, you must involve the hardware vendor in the planning and configuration. Microsoft Windows server products support up to eight buses per adapter, 128 target IDs per bus, and 254 LUNs per target ID. Adding support for more LUNs involves modifying the registry. See Chapter 5, Designing Highly Available Microsoft Windows Servers, for more information. Also keep in mind that your registry cannot grow infinitely large.
Logical Disk A logical disk is part, or all, of a volume carved out and formatted for use with Windows, and is usually represented by a drive letter. Some storage vendors use the word containers , which can contain multiple logical volumes that represent one logical disk to Windows. In storage vendor language, this might be referred to as a LUN, which is not how LUN is defined here.
Work with your hardware or storage vendor to ensure that you are both speaking the same language when it comes to your storage solution.