Continuous data protection (CDP) explained: True CDP vs near-CDP

Learn how continuous data protection (CDP) functions, compare true CDP and near-CDP, and find out who sells CDP and whether it can replace traditional backup.

Continuous data protection (CDP) is a form of data replication that copies data from a source to a target. True CDP does this every time a change is made, while so-called near-CDP does this at pre-set time intervals. Near-CDP is effectively the same as snapshotting.

Because true CDP copies all delta changes, a system can be restored to any point in time required. This can be especially useful if you need to roll back to a point before a corruption event took place, for example.

Because they depend on fixed-interval copies, near-CDP/snapshots only allow you to roll back to a given point in time. For this reason, true CDP offers a recovery point objective (RPO) of zero, while the equivalent for near-CDP/snapshots is the last time a copy took place.

Continuous data protection can be implemented in two main forms: software based with agents running on designated servers, or as a hardware-based appliance that can be in-band (in the data path) or out-of-band (outside the data path).

How does CDP work?

Continuous data protection works by copying changed data from the source system to a target. Often, this will be disk at the same site as the source, and this provides a method of effecting very quick recovery of data.

However, it is possible to replicate off-site and this clearly provides much greater protection and potential disaster recovery provision. With some CDP products you can replicate to two locations -- one on-site for rapid recovery and a disaster recovery site further afield.

True CDP systems record every write and copy them to the target where all changes are stored in a log. In case of a physical system failure, the continuous data protection system will have kept all changes up to the last write before failure, and you can restore to that point or to the last point before any corruption occurred.

True CDP systems will handle replication of files or applications with equal ease as they record every change.

By contrast, near-CDP/snapshot systems copy files in a straightforward manner but require applications to be quiesced and made ready for backup, either via the application's backup mode or using, for example, Microsoft's Volume Shadow Copy Services (VSS).

Can CDP replace traditional backup?

Continuous data protection offers nearly instantaneous recovery from disk and -- for true CDP at least -- an RPO that's as up-to-date as it's possible to be. Also, because CDP takes copies throughout the day, it's possible to escape the dreaded backup window. That means CDP offers the possibility of moving away from the single monolithic backup running overnight (and possibly into the next working day).

But can it replace traditional backup? Well, the potential success of any backup strategy is dependent on a few factors. Key among these is the distance between the backup copies and your primary site. If you're copying every single change using CDP, you potentially have a near-zero recovery point objective and a rapid restore time from disk, so you are well protected against scenarios short of a major disaster.

But if those copies are at the same site as the primary data, then in theory you're not protected at all in case of fire or other disaster. To achieve effective data protection with CDP you need to move copied data off-site, either by network or removable media.

So, the answer is yes, continuous data protection can replace traditional backup, but in most testing scenarios it's only as good as your ability to get backed up data off-site.

Who is using CDP?

Last year, carried out a purchasing intentions survey of 435 storage professionals from UK businesses with an average annual revenue of £1.1 billion. At the time, 13% of respondents said they had implemented CDP, 9% were planning on implementing it, 8% were evaluating it and 20% said they would evaluate it.

How to buy CDP

When CDP emerged, it was invariably as a standalone product offered by a niche player. As often happens, those companies and products were snapped up by the big players. CDP is now mainstream and incorporated into the software features of storage arrays, a feature of backup products or a separate product offered by storage/backups vendors.

Symantec, for example, acquired Revivio's intellectual property and later released its technology as NetBackup RealTime. IBM offered Tivoli Continuous Data Protection for Files and later, having bought FilesX, released TSM FastBack; EMC bought Kashya and then launched RecoverPoint.

Some examples of CDP products: 

  • BakBone Software NetVault:TrueCDP
  • CA XOsoft
  • DoubleTake Software Double-Take Backup-- near CDP, but can be upgraded to true CDP
  • EMC RecoverPoint
  • FalconStor Continuous Data Protector
  • IBM TSM FastBack
  • InMage Systems DR-Scout
  • Microsoft Data Protection Manager
  • Symantec NetBackup RealTime

CDP products for desktops and laptops 

  • Atempo Live Backup
  • Barracuda Networks BarracudaWare Yosemite FileKeeper
  • IBM Tivoli Continuous Data Protection for Files

Hosted service providers that offer CDP capability 

  • Asigra Cloud Backup
  • i365
  • Iron Mountain

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