SQL Server Reference Guide

Mar 28, 2003

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Over time, we all end up with more stuff than we often need. This is true not only in our personal lives but with our servers. Perhaps you’ve install a server, install another Instance, install another server, put a few Instances on that, and over time we’re not able to monitor them all to ensure that they are all being used to the fullest extent.

When we do finally take a look at the servers and Instances, we often find that some are not busy for a majority of the time, and others are suffering from performance problems. Averaged together, a quick examination shows that if everything were balanced appropriately, you could re-arrange the servers and even not have to use some of them (sometimes a lot of them), which saves maintenance, space, heat, money and licensing. A win-win all around. This is what a consolidation effort is all about — after all, since SQL Server is a database server, it stands to reason that all of the databases can begin to share resources. This is one way to consolidate, and there are others that I’ll cover in this tutorial.

Monitoring and Documentation is Critical

I’ve written another tutorial that teaches you how to create an Application Profile, which is something you should take a look at before you even start to do your consolidation. While it might be tempting to start with the database side of the equation, the application is what drives the growth, criticality, risk and so on. It’s all in that article, so make sure you check it out and set up that application matrix for the rest of this tutorial.

With the information from that matrix, you know which applications are heavy users of the four parts of the system: CPU, memory, I/O and network. You should consolidate opposite applications onto the same system — meaning a heavy I/O application should be placed with one that uses CPU, network or memory more than I/O.

But that’s not the end of the story. Since all of the methods I’ll explain here end up placing more databases on one server, there’s a higher level of risk. That means you need to give more thought to the way you back up, secure and protect those systems. Placing all of your top-tier applications on one server is risky — it’s better to spread those out to multiple servers, combining them with less critical applications.

What follows is a list of options that you have to combine the databases for your applications. You should start at the first, and if your application meets the criteria, use that method. If you have other needs, move to the next option.

Application Stacking

Application stacking is the process of finding applications that have the same data needs, and combining them into a single database. For instance, after you do your application profile, you discover that application A and application B actually perform the same work, perhaps with the differences of only a few fields or tables here and there. In this case, you can simply modify the applications to use the same database.

This isn’t trivial — there are real considerations here, but I once found two applications that not only did much the same thing, but they even had an Extract, Transform and Load (ETL) process that sent each other the data! In this case I saved not only space in the database, but the new merged system eliminated the ETL process, saving even more time, space and effort.

Your application profile process will help you locate these applications.

Criteria:

You have control over the applications, and can change them
You have control over the databases, and can merge them
Security between the applications is not an issue
The business accepts the combined application

If you don’t meet these criteria, then it’s time to move on to the next option.

Database Stacking

While you may be able to find an application or two that performs much the same work, you may not be able to change the application or allow the same database to be used for both. In this case, your next option is to place more databases on the same installation (Instance) of SQL Server. This is called “Database Stacking,” and it is one of the most overlooked methods of consolidation I see.

The advantages here are that you’re running on the “bare metal” of the system, you have undiluted access to memory, CPU, I/O and networking subsystems, and the Instance is only carrying the load of itself.

There are downsides — for one, each Instance of SQL Server shares a single tempdb system database. That can become a bottleneck. Also, some applications have a security barrier that you need around them. Finally, the databases may need different service packs of SQL Server or the operating system installed.

Criteria:

You can’t use application stacking
You have enough resources (CPU, memory, I/O, network) on the destination Instance of SQL Server to host more databases
tempdb is not a bottleneck
The databases can tolerate the same service pack of SQL Server and the operating system
You can segment the security for the Instance in a way that allows the databases to be on the same server
You can use the same Instance-level settings in SQL Server for all databases

If you don’t meet these criteria, then it’s time to consider using an Instance strategy.

Instances

If you have needs to wall off the security, tempdb or service packs for the databases, you should consider installing SQL Server again on the same system. Doing so creates another Instance of SQL Server, and allows you to have a different tempdb database, a different service pack level (of SQL Server, not the operating system) and different system administrator (sa) accounts.

With another Instance, you can also configure the settings to be different. Depending on your edition of SQL Server, you can create up to 50 Instances on the same server.

Criteria:

You can’t use application or database stacking
You have enough resources (CPU, memory, I/O, network) on the destination Instance of SQL Server to host more Instances
Your edition supports the number of Instances you want to install
You have enough separate drives to move out the tempdb, data, logs and indexes (at a minimum) for each Instance’s databases
Your databases can tolerate the same operating system security, service pack level and configuration

If you don’t meet these criteria, then it’s time to consider using Virtualization.

Virtualization

Virtualization is creating multiple systems inside a physical computer using only software. Many people consider this the first line of consolidation, but I consider it the last, for multiple reasons.

Whenever you virtualize a computer, it emulates the various functions such as CPU and memory, and as such has to pass through another layer of software to do that. This will slow down the system, even if only slightly.

Even if the system performs well in Virtualization, you’re carrying the “weight” of multiple operating systems. This is going to add to the overall load of the system.

To be sure, there are reasons other than performance to use virtualization. Virtualized machines are largely hardware-independent, they are easily moved, simple to back up and so on. So you may have a reason to use virtualization other than just consolidation.

Even so, be aware that in most cases for consolidation for your data systems, you don’t always gain the biggest impact using this method. And you add a great deal of complexity.

Criteria:

You can’t use application or database stacking, or install more Instances
You have enough resources (CPU, memory, I/O, network) on the destination Instance of SQL Server to host the Virtual Machines
You need a full operating-system level of service packs, security, and settings for the system
You have a plan to monitor, manage and maintain the additional systems
You have considered risk factors for putting multiple machines on a single physical device

Take these suggestions, and lay out your applications to ensure you know the variables. Apply the choices from above, keeping in mind the criteria as you go.

InformIT Articles and Sample Chapters

More information on choosing to virtualize servers is in the article Windows Server 2008 Hyper-V Technology Primer.

Books and eBooks

Marty Poniatowski has a great treatment of this topic in his book Foundations of Green IT: Consolidation, Virtualization, Efficiency, and ROI in the Data Center.

Online Resources

There are some more great hints on this process in this article series.

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