Replication Products

Like any technology, replication products have a downside: Managing another software package means spending more time setting up replication, especially if you stream to tape. You also must be concerned with bandwidth: Straight copies of data will hog your pipe and slow down production systems, so you must know how well the system handles replication of partial file changes before you buy.

Back Up Replication Copies

If you're streaming to tape from the target machine, find a system that lets you schedule "suspended" replication, which temporarily stops disk writes to let the backup complete consistently. That's another schedule you'll have to maintain, so be aware of the time commitment. Vendors such as EMC Corp., Hitachi Data Systems, Maranti and XOsoft offer hardware or software products that allow suspended replication. Several error-logging and notification options are available; make sure your vendor can accommodate your existing architecture.

For remote offices, take note of how much bandwidth the replication system uses and how well it handles management without IT staff on site. Most replication systems can run months or even years without IT intervention once they're configured, but it's worth checking before you buy. Most also allow remote or centralized management with Web interfaces.Some systems have consistency problems with backups, particularly databases and e-mail that have a high volume of changes in a binary file format, with changes not always written directly to the data store. If you're replicating database products and e-mail, make certain the product you choose will protect them--most vendors require a separate license for each of these.

As with all products that claim to back up your data, the versatility and reliability of restores are major issues. Check with your vendor about point-in-time recovery, which lets you restore your data to the way it was just before your system became corrupted. Many replication products offer more granular restoration than tape provides and let you go to a specific point in time. Most of the vendors that supplied product information for our (Interactive Buyer's Guide charts) offer configurable granularity using snapshots of your replicated environment.

If you need something even more granular, consider a CDP (continuous data protection) product, which offers constant tracking of every change made in the file and lets you reconstruct the file to any point in time. Replication granularity isn't worth its salt unless it meets the specific needs of your organization. Can you choose the state of a file up to the second, minute or 10-minute mark? A CDP product offers maximum flexibility--it lets you restore a given file to any point in its lifecycle.

Configure First, Relax Second

The management interface is arguably one of the more important portions of the overall replication system. Don't skimp on it. It's important to be able to choose the machines being replicated, where they're replicated to, how granular those replications are, and if or when the replications are suspended to make time for streaming to tape. If you can't use the management console, the replication system is useless. Get a demo before you buy.While you're evaluating the management interface, consider ILM (information lifecycle management) as well. If your replication system can list all the files in your network--or even on a target machine by modification date, and frequency of modification and access--it may help you in evaluating retirement of expired files and moving them off to cheaper storage solutions. Much of this information must be maintained by a replication system to adequately replicate. Find out if the product you're considering offers this information in the form of reports. If you don't want to buy more storage than you need, it's worth checking out the "nonperformance" reports available in vendor replication products because they can help determine which files must be deleted and which storage is underutilized.

Volume of data transmitted is important, too. Once the base file or disk has been replicated, many vendors send only changes to the data, not the entire file. Although the level of replication is more essential in a WAN or busy LAN environment, it's an important consideration in any environment.

There's a trade-off when you accept a level of replication: Systems that copy only modified bits of a file might use less bandwidth, depending on your system's usage patterns and the overhead associated with each replication, but they might not. Bit-level replication isn't new, but most of us are more comfortable with byte-level replication because we believe it's more reliable. The benefits of bit-level replication depend on implementation and usage. In general, products that offer byte-level replication are the most prevalent on the market because users want effective solutions at the level the machine works. Most of the products listed in our Interactive Buyer's Guide charts operate at byte-level, with some handling file level and only a few offering bit-level replication, so check before you buy. Some systems listed do file- or block-level replication--and these have a lot of overhead--so consider the bandwidth implications of transmitting an entire file for one or two changed bytes.

Make sure your operating systems are supported. Most data-replication products require software to be installed on either the source or destination machine. Buying multiple solutions to support disparate platforms just isn't worth it. Simply put, each product you purchase adds hours of work, so factor in all costs for all products. The days of "one for Windows, one for Linux, one for Solaris" must fall behind us as we are asked to do more with less.

Megabucks for Megabits?The final item to consider is price. Do you pay by the server or by the volume of data being backed up? Does buying one product lock you into that particular vendor's storage solutions down the road? Figure out the licensing and pricing, and be sure you're getting what you need and expect.

Don MacVittie is a senior technology editor at Network Computing. Previously, he worked at as an application engineer WPS Resources, a Green Bay, Wis., utility- holding company. Write to him at [email protected].

Replication Checklist

Before you buy a replication product:

1) Find a system that lets you schedule "suspended" replication.2) Know what you're going to replicate, and get a specific price quote.

3) Ask your vendor if point-in-time restores are available.

4) Don't skimp on the management interface, and get a demo.

5) Be sure the product will run on your operating systems.

For details and prices on specific systems, use our Interactive Buyer's Guide charts.0