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September 15, 2008


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W. Curtis Preston

I agree with your overall premise. CDP's not replacing backup anywhere that I know of, nor do I see that happening any time soon -- actually for different reasons than what you stated. My reasons have to do with it just being too different than what people are used to. Dedupe hardware is a nice enhancement to the backup software I'm using, and dedupe software is a different software that works on the surface just like my old backup software, but does cool things under the surface. (It still does nightly backups, etc.) But CDP is just, well, weird. ;) It's very different and a much bigger pill to swallow. I'm not saying it's not better. I'll compare it to teleportation. If such a thing existed, then it would be way cooler than cars or planes. But it would be new and scary. CDP is teleportation to me.

I do not beieve that CDP will necessarily be the same or larger than traditional backup. Your math is fine, but it only works if you have records that are being updated 100s of times a day. I'm not sure that's a normal use case. The second issue is that it doesn't take into account the fact that CDP is block based, and backup is typically record and file-based. While only 1% or less of blocks typically change per day, a typical incremental backup is 10% or more. That's because it backs up files and records that have changed, not the blocks. This is where a lot of the dedupe savings come from. I'm not saying that CDP will always be less, but I disagree that there is enough evidence to say that it will always be more. I would need more evidence to believe that.

I also disagree that dedupe can't change your RPO. If your backup system can handle quick backups, then you can absolutely back up more often each day than you did before. If you're replicating (since you're deduping), you can even decrease your DR RPO.

Finally, the CDP product that EMC acquired (Kascha) already has the ability you're describing. You can start out capturing everything, then drop to significant points in time.

Good post.

Scott Waterhouse

You know, I was chatting internally with someone about why Oracle dbas are less likely to embrace deduplication than other people. My conclusion was that they are very conservative. Sometimes I wonder if it isn't just teleportation that we (backup people) end up rejecting. I think it is many forms of change. To extend the transportation metaphor: would we even embrace a hybrid? Or is the old gas guzzler "good enough"?

But I couldn't agree more. CDP is just too much of a change of paradigm. I think things need to be more obviously broken before we embrace change. Tape is relatively broken, and that is why virtual tape and deduplication has been so successful.

And your reasoning about capacities is correct. I was just trying to highlight that CDP will require more storage than dedup--how much more depends on the rate of change. It will definitely be less than traditional backup.

Which means that it won't be capacity savings that will incent people to move to CDP. There has to be some other radical or unique value proposition that CDP offers. Which could also well be some dramatic failure on the part of traditional backup applications to offer what users want, or what is necessary. (One of the reasons Avamar has been so successful, in my opinion.)

For those that are interested, information on EMC's CDP product can be found here: http://www.emc.com/products/detail/software/recoverpoint.htm


Interesting article but clearly you have not implemented or thoroughly evaluated a true CDP solution. I have several clients that utilize CDP and currently selling Falconstor product after internal bake-offs. The key with CDP is that changes are recorded at the block level or in the case of Falconstor's CDP the sector level. This minimizes impact on the disk and more importantly the network in which backup is taking place compared to a traditional backup. So not only is disk space being saved but backups occupy less production time and require fewer CPU cycles than traditional backup.

Most CIOs would agree that improving backup times, RPO, and RTO are way more critical than saving 10% on disk space especially if that disk can be tier 2 disks. In an optimized CDP environment you can actually journal IO changes to fast disks and sequentially dump them to a second tier disk. This is a great way to save money but also must be considered when looking at a recovery.

Secondly all of the true CDP products I have evaluated have a scheduling system (some better than others) to span out recovery points. I have customers maintaining multiple years for an archival purpose while keeping hourly and daily points in time in place for more immediate recovery needs. I assure replacing backup with CDP will not multiply your disk requirements anywhere remotely close to your quick thought out demonstration above if deployed correctly.

Lastly, I agree as well that tape is not out and that is another reason we side with one vendor for CDP is the ability to archive backups to tape while still reaping the benefits of immediate recovery, bare metal recovery, and minimized disk occupation.



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