If you're a user or system administrator pondering the use of Subversion, the first question you should ask yourself is: "Is this the right tool for the job?" Subversion is a fantastic hammer, but be careful not to view every problem as a nail.
As a first step, you need to decide if version control in general is required for your purposes. If you need to archive old versions of files and directories, possibly resurrect them, and examine logs of how they've changed over time, then version control tools can do that. If you need to collaborate with people on documents (usually over a network) and keep track of who made which changes, a version control tool can do that, too. In fact, this is why version control tools such as Subversion are so often used in software development environments—working on a development team is an inherently social activity where changes to source code files are constantly being discussed, made, evaluated, and even sometimes unmade. Version control tools facilitate that sort of collaboration.
There is cost associated with using version control, too. Unless you can outsource the administration of your version control system to a third-party, you'll have the obvious costs of performing that administration yourself. When working with the data on a daily basis, you won't be able to copy, move, rename, or delete files the way you usually do. Instead, you'll have to do all of those things through the version control system.
Even assuming that you are okay with the cost/benefit tradeoff afforded by a version control system, you shouldn't choose to use one merely because it can do what you want. Consider whether your needs are better addressed by other tools. For example, because Subversion replicates data to all the collaborators involved, a common misuse is to treat it as a generic distribution system. People will sometimes use Subversion to distribute huge collections of photos, digital music, or software packages. The problem is that this sort of data usually isn't changing at all. The collection itself grows over time, but the individual files within the collection aren't being changed. In this case, using Subversion is “overkill.”[2] There are simpler tools that efficiently replicate data without the overhead of tracking changes, such as rsync or unison.
Once you've decided that you need a version control solution, you'll find no shortage of available options. When Subversion was first designed and released, the predominant methodology of version control was centralized version control—a single remote master storehouse of versioned data with individual users operating locally against shallow copies of that data's version history. Subversion quickly emerged after its initial introduction as the clear leader in this field of version control, earning widespread adoption and supplanting installations of many older version control systems. It continues to hold that prominent position today.
Much has changed since that time, though. In the years since the Subversion project began its life, a newer methodology of version control called distributed version control has likewise garnered widespread attention and adoption. Tools such as Git (http://git-scm.com/) and Mercurial (http://mercurial.selenic.com/) quickly rose to the tops of the distributed version control system (DVCS) ranks. Distributed version control harnesses the growing ubiquity of high-speed network connections and low storage costs to offer an approach which differs from the centralized model in key ways. First and most obvious is the fact that there is no remote, central storehouse of versioned data. Rather, each user keeps and operates against very deep—complete, in a sense—local version history data stores. Collaboration still occurs, but is accomplished by trading changesets (collections of changes made to versioned items) directly between users' local data stores, not via a centralized master data store. In fact, any semblance of a canonical “master” source of a project's versioned data is by convention only, a status attributed by the various collaborators on that project.
There are pros and cons to each version control approach. Perhaps the two biggest benefits delivered by the DVCS tools are incredible performance for day-to-day operations (because the primary data store is locally held) and vastly better support for merging between branches (because merge algorithms serve as the very core of how DVCSes work at all). The downside is that distributed version control is an inherently more complicated model, which can present a non-negligible challenge to comfortable collaboration. Also, DVCS tools do what they do well in part because of a certain degree of control withheld from the user which centalized systems freely offer—the ability to implement path-based access control, the flexibility to update or backdate individual versioned data items, etc. Fortunately, many wise organizations have discovered that this needn't be a religious debate, and that Subversion and a DVCS tool such as Git can be used together harmoniously within the organization, each serving the purposes best suited to the tool.
Alas, this book is about Subversion, so we'll not attempt a full comparison of Subversion and other tools. Readers who have the option of choosing their version control system are encouraged to research the available options and make the determination that works best for themselves and their fellow collaborators. And if, after doing so, Subversion is the chosen tool, there's plenty of detailed information about how to use it successfully in the chapters that follow!