Preparing to Make Resources Available Offline

By Brien M. Posey | Dec 14, 2000 | Print this Page

I've always heard the saying, You can't take it with you. Whoever came up with this phrase obviously wasn't talking about mobile computing in a Windows 2000 environment. Today, notebook computers have more hard disk space than desktop computers had only a year or two ago. For example, the 18 GB of hard disk space on my notebook was unheard of just a short time ago.

The vast quantities of hard disk space on today's notebooks, and the power of Windows 2000 make it possible for mobile users to take network resources such as files, folders, and even entire Web sites with them when they're on the go. Mobile users can work with these resources while offline, just as if they were connected to the network. When mobile users return to the office, any changes that might have been made are synchronized between online and offline copies of the resources when the mobile user reconnects to the network.

In this article series, I'll discuss the procedure for making various network resources available offline to mobile users. As I do, I'll also discuss some serious issues that you'll encounter when doing so, such as those related to synchronization, performance, and security.

Do You Have Sufficient Space?

Before I discuss the procedure for making network resources available offline, let's take a moment to discuss what's actually going on when you do so. As I mentioned, the process is greatly dependent on adequate hard disk space. Therefore, it should come as no big surprise that the process involves creating a cache on the notebook's hard disk. Windows 2000 is designed to access files and folders from the cache when the user is offline, but to make it appear to the user as though the files and folders were being accessed directly from the network.

This process sounds good in principle, but there are a few things that you'll have to consider. The first issue that you'll have to consider is space. For example, as I mentioned, my notebook has 18 GB of hard disk space. Even though the Windows 2000 operating system and my applications consume some space, let's assume for the sake of simplicity that I have the entire 18 GB available for caching network resources. Now consider that my primary file server contains 180 GB of hard disk space. Needless to say, my notebook would only be able to cache about a tenth of my server's total capacity. Therefore, you can't simply cache an entire server or an entire network. Instead, you need to be selective about which files and folders you plan to cache.

Not only do you need to make sure that you're not downloading too much content to mobile users now, but you also need to plan for later. For example, suppose you have a rapidly growing directory that needs to be made available offline. The growth rate of this directory should be taken into account so not to overwhelm the offline cache.

What Resources Should be Made Available?

Fortunately, capacity planning isn't entirely your responsibility (of course, in the world of systems support, everything is ultimately the administrator's responsibility). It's up to you to designate which files and folders can be made available offline. However, it's up to the individual user to decide which of the available files they actually want to use offline. Even though the user decides which files to use offline, don't take your part lightly. I've known a couple of administrators who simply make everything available offline. However, you might think twice about making confidential or other sensitive data available for offline use.

Pros and Cons of Automatic Caching

You must also take care to specify the method of making data available offline that makes the most sense for your organization. Any time you make a file or folder available for offline use, you're presented with three choices for how to do so: Automatic Caching, Manual Caching, or Automatic Caching For Programs. Each of these choices has its own advantages and disadvantages. You must carefully consider these advantages and disadvantages to determine which type of caching is most appropriate for each resource.

Automatic caching is the simplest type of caching. Any time a user opens a file that's been designated as available for offline use, the file is automatically added to the user's cache. Although this method sounds great, it has some drawbacks. For starters, automatic caching isn't good for people who tend to use a lot of different filesregardless of the file size, caches tend to fill up over time.

To illustrate why this is a problem, consider what would happen if you have a file that you need to use offline. You open the file to cache it. Now, suppose you work with several other files over the course of the day that are also designated as being available offline. As you work with these files, they are also added to the cache. Eventually, the cache may fill up. Obviously, when this happens, something has to go. To decide what stays and what goes, Windows uses an algorithm that looks at which files are used most frequently and which files were opened most recently. If the file you really needed hasn't been opened recently and you haven't done much work with it yet, there's a good chance that it could be discarded from the cache, meaning that it won't be available offline when you need it.


The other reason automatic caching isn't good for large numbers of files is that it only caches files that you've opened. Suppose you need offline access to an entire folder or group of folders. In such a situation, you'll have to open every file in the entire folder structure to make the structure available offline, and then hope that you didn't fill up the cache along the way.

As you can see, automatic caching is best suited to users who need constant offline access to a few select documents. Later in this series, I'll explain how such users can avoid accidentally filling their caches with unwanted documents by caching only the documents that they specifically need. In the next article in the series, Part 2, I'll explain the pros and cons of manual caching and automatic caching for programs. //
