I keep reading all kinds of articles and tweets like this one from Robin Harris that predict or announce the death of parity-based RAID. (Not everyone agrees, of course.) The ultimate worry is that a second disk would fail while a RAID 5 group is rebuilding, or a third disk would die while a RAID 6 group is rebuilding, causing data loss. The bigger disk drives get, the long rebuilds take, and the bigger the chance that this would happen. This paper published at Usenix geeks out as much as you could possibly want on the subject.
At the same time all of that is happening, we keep making bigger and bigger datastores that store everything from Oracle/SQL/DB2 to hundreds of VMs stored on a single large volume. The company that had a mission-critical 300 TB database comes to mind.
All I’m saying is that when we’re talking dozens to hundreds of terabytes of data in one place, at some point traditional backup is not going to cut it. I don’t care how fast your tape drive or favorite disk target is (deduped or not), at some point a restore of any kind is just not going to meet your RTO.
Here’s my next thought. When we think about double or triple disk failures on a critical storage array, that sounds really bad. But what if — in the extremely unlikely event this really bad thing happens to you — you just flip a switch and you’re now running operations from your backup system, that has a very recently updated copy of your data? If it’s a true CDP system, you might not lose any data at all. If it’s a near-CDP system, you might lose a few minutes or an hour. It’s all about what you’re willing to pay for.
- If you’re not thinking about CDP and near-CDP solutions, you should be.
- Does the idea of a CDP or near-CDP system take away a little bit of the sting of the fear of the death of RAID?
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Written by W. Curtis Preston (@wcpreston). For those of you unfamiliar with my work, I've specialized in backup & recovery since 1993. I've written the O'Reilly books on backup and have worked with a number of native and commercial tools. I am now Chief Technical Architect at Druva, the leading provider of cloud-based data protection and data management tools for endpoints, infrastructure, and cloud applications. These posts reflect my own opinion and are not necessarily the opinion of my employer.