Sunbelt SoftwareDouble-Take 4.4 SP2 review

Tape-based server backup is still the most cost-effective method of protecting critical data. But, by its nature, it can only ever provide a point-in-time copy for restoration purposes. Symantec recently spotted an opening here and added a real-time backup component to its Backup Exec 10d. However, Sunbelt's Double-Take benefits from being built from the ground up specifically to provide data replication and failover services for Windows servers.

Double-Take is designed to augment tape-based backup, not replace it. It works by replicating selected data on source servers to target servers that can be in the same locality or at a remote site. Once the source data has been mirrored, Double-Take monitors the target for any modifications and secures the changes, or deltas, in real-time.

To create Replication sets, you can use the management console on any system. This will allow you to remotely select the drives, folders and files on the source server you want to protect, and then fire up the Connection Manager and choose the target server. The source folders may be mapped directly to the same location on the target server or you can choose a custom destination. A Text Client utility that's run from the Command Prompt may also be used to define target files and folders, as well as to manage and monitor Double-Take operations.

The initial mirroring process is swift. Office documents totalling 630MB were copied to our test target server over Gigabit Ethernet in less than three minutes, while a 5GB collection of business data and documents was mirrored from a Windows 2000 Server source to a Server 2003 target in 24 minutes. Bandwidth restrictions can be applied to each individual replication task, making Double-Take highly suited to slower WAN links. You can pick the link speed and specify a percentage the job is allowed to consume. A new feature introduced in this version is the option to apply a schedule to determine the times and days when the restrictions should be applied.

Restoring files is also simple. First, you disconnect the relevant target and source servers, and then run the Restoration Manager. After selecting the appropriate servers, you may choose the backup target files and where you want them restored. Only directories can be selected, but you can opt to overwrite all files or restore backup copies that are newer than the original.

The failover features will prove valuable. You're able to monitor a source system using the Failover Control Center and, if it fails, the selected target system can take over and assume the target's name, IP addresses and network shares. We found it easy enough to set up a basic system failover job, but you'll need to get your hands dirty with scripts if you want application failover as well. There are plenty of examples available for most popular applications on the support website. These will need to be tweaked to your needs and we recommend testing them thoroughly before going live.

We've seen more than a few real-time D2D (disk-to-disk) server backup products come and go, but Double-Take has more than lasted the course. Failover is complex to set up, but the mirroring and replication features alone make this a valuable asset for data security

Author: Dave Mitchell