Understanding RAID Systems for Surveillance Storage

A tutorial on RAID data storage architectures, and how they apply to video surveillance

In recent years, the physical security industry has seen more changes than just about any other time in modern memory. Digital or IP (Internet Protocol) cameras, based on CCD technology, have replaced more familiar analog surveillance cameras in most new installations. And to support them, DVRs (Digital Video Recorders) have virtually eliminated the use of tape and VCRs.

Combined, these two IP technologies have opened the way for the physical security industry to dramatically improve video surveillance and other common applications while greatly reducing costs and increasing service levels.

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IP-based video surveillance storage was the topic of a recent webinar from SecurityInfoWatch.com. You can register to view this archived webinar for free.

Yet moving to IP also has its own challenges, especially as security users come to rely more and more on the improved resolution, higher frame rates, and megapixel quality that the technology offers. In fact, many security practitioners and integrators admit that over half of their support and customer satisfaction problems relate to DVR drive failures, which can result in the loss of all recorded video and data.

So is it a mistake to move from tape to IP? The answer is a resounding "no", as the benefits of scalable, open IP far outweigh the problems. In fact, most IP storage problems in DVRs can be either fully eliminated or the risk mitigated with the application of basic techniques and strategies that are common in the Information Technology (IT) industry.

One way to avoid data losses is to use RAID technology, either built into the DVR system or added on as an external IP storage array.

What Is RAID, and Why Do We Need It?

RAID is the acronym for Redundant Array of Independent (or Inexpensive) Disks, in wide IT use since the late 1980s and as defined in the SIGMOD paper, "A Case for Redundant Arrays of Inexpensive Disks". The Storage Networking Industry Association (SNIA) defines RAID in part as "...a family of techniques for managing multiple disks to deliver desirable cost, data availability, and performance characteristics to host environments."

And like many families, not all members are suitable - or desirable - for every need or situation. Nowhere is that more true than in physical security for video surveillance. In fact, some RAID levels would be extremely bad choices for our industry.

To determine which RAID makes the most sense for video surveillance, let's take a quick look at the basic techniques, strengths, and weaknesses of each.

An Overview of RAID Levels

RAID 0 provides no redundancy or data protection from the failure of any disk. So why use it? For our purposes in physical security, you shouldn't. But in IT there are some specific situations where the absolute best speed is more important than protecting data. RAID 0 delivers just that, by splitting or "striping" the recorded data across all of the drives in the array so as to improve read/write times and effectively spreading the load. RAID 0 was not one of the original levels adopted by the IT industry, but was added later specifically to deliver this improved performance capability.

Since losing any drive in the array to a failure would result in ALL recorded data being lost, this is not a suitable technique for use in physical security applications in general and video surveillance storage in particular.

RAID 1 is also referred to as a 'storage mirror' or a 'mirroring solution'. All data is recorded on not just one but two identical drives, so that two copies exist at all times. If one drive fails, the exact copy on the other continues to function and no data is ever lost. While many DVRs have no RAID protection at all, some do feature RAID 1 support.

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