Companies are moving away from traditional tape- or even disk-based backups that can come with recovery times measured by a calendar instead of a stopwatch. An increasing number are turning to data replication and continuous data protection, letting them bounce back from a disaster in hours and, in some cases, even minutes.

Replicating data locally or across the WAN to a disaster recovery site in real time isn't new--companies with the big bucks to implement it have been doing this for years. What has changed in the last few years is that this higher level of protection is increasingly affordable and accessible to more companies; it's now well within the reach of small businesses.

Lower initial costs for hardware, software, and services are making continuous data protection more affordable, as are technologies and services that significantly lower ongoing monthly charges. These include everything that makes it more efficient to send data across the wire, from compression and deduplication to WAN optimization.

Technologies such as compression and deduplication can decrease data traffic and significantly reduce bandwidth requirements and overall costs. While deduplication and compression allow more efficient use of available bandwidth, bandwidth itself is becoming cheaper--yet another driver in increasing the affordability of these options. Better and cheaper WAN acceleration products and technologies are also playing a role by allowing much more efficient use of available bandwidth. That enables replication across a smaller and lower-cost link. It also may allow faster recovery from a problem.

But replication has a dark side as well. If you have corruption in data at your primary site--due to hardware or software problems, user error, or other problems--you might replicate that corruption to the secondary site as well. That's not what you're looking for from a disaster recovery system. You need something that protects against that corruption, and that's where continuous data protection, or CDP, comes in.

What is CDP? There's some disagreement as to what qualifies as true CDP and what may be more appropriately called "near CDP." The CDP group within the Storage Networking Industry Association defines it as continuously capturing or tracking "data modifications and stores changes independently of the primary data, enabling recovery points from any point in the past." CDP systems may be block-, file-, or application-based.

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