Product Reviews

Doing a Server Double-Take

Despite its lackluster support, Double-Take may be the safety net you need.

• By Suzanne Pacheco
• 08/01/2002

Value—A. If you wanted to set up failover in Windows 2000 without Double-Take (or other third-party software), you need to buy Windows Advanced Server, along with an external RAID array or other external storage unit. This can get pretty expensive; in comparison, the $2,495 price tag for Double-Take is a real bargain. One caveat: You must purchase licenses for each server you install Double-Take on, even if a server will be used strictly for failover.

Installation and set-up—B+. The installation process is clean and simple—just run autorun.exe and follow the defaults. The connection wizard guides you through setting up replication and failover (See Figure 1). For simple data file protection, specify the data directory on the source you want protected, as well as a directory on the target to which it should be mirrored. Double Take takes care of the rest.

Setting up failover for SQL Server is just a tad more complicated. You have to set the SQL services startup to “manual” and set up Double-Take to run pre- and post-failover batch files.

During installation, you’re given the option of starting the Double-Take service automatically or manually. If you specify manually and try to start Double-Take later without starting the service, you’ll get a completely unhelpful error message. This is certainly easy to troubleshoot, but a message like, “The Double-Take service is not currently started. Would you like to start it now?” would be nice.

Functionality—B. Security for Double-Take is based on NT security, rather than a separate application login and password. Great! One less password to remember.

Failover works wonderfully for basic data file protection. The target server creates the shares and assumes the machine name and IP address of the failed source server. To test this, I opened a Word document on a source server from my workstation. I then shut down the source server while editing the document. The failover process was invisible, and I was able to continue to edit and save the document. The only minor issue is that, by default, there’s a 25-second window after the source server fails and before failover occurs (you can change this setting). I tried to save during that time, and there was a short delay while the system searched for the server, after which I was prompted to save to my default local data directory.

To test SQL Server failover, I connected to a SQL database from linked tables in Access on my workstation. I opened a table and started editing, then shut down the source server. I was able to continue to read and edit the table, but couldn’t save changes or open another table. I had to shut down and restart Access to continue.

Documentation—D. Double-Take’s documentation is occasionally inaccurate and generally very frustrating. The User’s Guide emphasizes that it assumes the administrator doing the installation has a certain baseline of knowledge. Fair enough, but that shouldn’t be an excuse for poorly organized or incomplete documentation.

You have to download additional documentation from NSI’s Web site if you’re setting up anything outside of a basic data file failover. This is in addition to a 538-page User’s Guide and 40-page Installation Guide.

While I’m on my documentation soapbox, one last point: The documentation is copied to Double-Take’s installation directory. It bothers me that the installation process doesn’t put shortcuts to the PDF files in the start menu.

Service—F. My experience communicating with NSI was not positive. I was disconnected, dumped into voicemail and never got a return call. I want to point out that I know what it’s like to work on the phones, and I was polite and courteous to the people I spoke with at NSI. I just got the impression they didn’t really care whether or not I was helped.

The connection wizard in Double-Take makes setting up failover simple and straightforward.

So what’s the final evaluation? In my case, Double-Take was being evaluated for potential use on our corporate SQL Servers. The so-so SQL failover performance, frustrating documentation and bad support experience prompted me to buy a different product. On the other hand, I was talking to a very knowledgeable colleague about a Microsoft Exchange issue; without being prompted he started raving, “…and we use this great product on our Exchange servers. It’s called Double-Take.” He loved it, without reservation. So, if you don’t mind the documentation and support issues, Double-Take might be the product for you.