Scripting DFS

Distributed File System (DFS) is becoming increasingly popular as a way to present users with a link to resources without regard for the actual back-end storage location. As the Microsoft article "How DFS Works" (http://technet2.microsoft.com/WindowsServer/en/Library/a9096e88-1634-4da6-b820-537341d349061033.mspx) explains, DFS lets you create a virtual view of shared folders through a namespace that an administrator creates. Users can view the namespace without needing to know where the data resides, regardless of whether it's on a Windows server or a non-Windows storage device. Because of DFS's increased popularity, I'm getting more frequent questions about how to script configuration and reporting of DFS. Fortunately for script writers, Microsoft provides several command-line tools that you can use to configure and query DFS. (For details about these tools, see the sidebar "DFS Scripting Tools," linked above.) However, these tools can return a lot more information than you really need. For example, most systems administrators and backup operators simply need to know the locations of specific back-end servers so that they can restore accidentally deleted files. To address this need, I wrote the DFSReportBuilder.bat script, a tool that will help you get valid output on the back-end target server locations that your DFS links are really pointing to. Using this script will make it easier for systems administrators and backup operators to locate backups that require restoration.

Listing 1 shows an excerpt from DFSReportBuilder.bat. You can download the complete script by clicking the Download the Code Here button above. I tested this script on a Windows XP Service Pack 2 (SP2) node running in a Windows Server 2003 domain. Always be sure to test your scripts in a development environment before deploying them in a production setting.

Requirements
The basic requirements for the DFSReportBuilder.bat script are that we capture all the DFS links and send an email message containing those links and the back-end server locations that the links map to. The Dfsutil.exe tool offers a switch option, /Export, for exporting the results to a file, but unfortunately, the export mode generates some XML output that isn't useable in the email message. Consequently, DFSReportBuilder.bat instead uses the /View option to capture and filter the output before using the Blat public domain command-line email program to send the report to a recipient list. The report format that we want the script to produce will contain only header information, the date of the report, and the DFS root name. Each line in the report will include the root name, link name, and target-server locations. If a link has more than one target-server location, the additional locations will appear on subsequent report lines. Although the Dfsutil.exe tool output contains the information we need, the output will require some massaging to yield the specific information we want for the email report. Let's look at four simple steps that will help you think through data filtering.

Step 1: Identify Important and Trivial Information
The first step in determining how to filter command output is to identify the information you need. I generally start by redirecting the command from my chosen tool (in this case, Dfsutil.exe) to a text file by using syntax such as:

DFSutil.exe /Root:\\Sales\ 
  Reports /View>C:\DFS.txt 

An examination of the output reveals a series of entries that include a line containing the link name and one or more lines with the target server or servers that are the back-end location of the data. Also, the output includes a line that gives us the DFS root name.

Step 2: Determine Your Filtering Execution Strategy
There are two basic ways to handle filtering. One way is to process the command output one line at a time, getting it into the format you need as it's coming from a file or For command. The second way is to use a batch technique in which you capture some or all of the command output in an array or file and process it all at once.

For this article's example, we'll first use a temporary file to hold the original output, as the sidebar "Arrays and Temporary Files," explains. Then, in the DFSReportBuilder.bat script, we'll use a two-stage filter. First, we'll use the batch strategy, as the code at callout C in Listing 1 shows. Second, we'll use the single-line approach, as the code at callout D shows.

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