Wednesday, May 14, 2008

Value of Stored Video

How precious is your stored video? Not very? Quite a lot? Very important, mission critical or drop dead important? These are the kinds of vague answers we hear that reflect your attitude toward risk. And that attitude drives the dollar value you are willing to invest to avoid losing the video you have gone to great lengths to capture and archive away for that rare incident review moment when it magically becomes more than just video - momentarily it becomes unimaginably precious.

This question is much harder to answer than it first seems, and understanding your options will help you make the right investment that suits your needs.

Hard drives follow Moore's Law - doubling in capacity or halving in price every 18m or so. This means that the 120GB hard drives of 3 years ago were tiny compared to the 750 GB and 1TB that are available now with 2TB drives around the corner. This technological driver has one major impact. Five years ago some customers could only afford low quality video which had lower resolution and frame rates. Now, customers are recording video for longer, a month instead of a week, 3 months instead of 1. Some customers, often regulated, store their video for a year, 3 years or even 5.

DVRs invariably have storage inside the box and you can easily buy DVRs with 2-3TB inside the box. If these hard drives are not configured with redundancy then if a hard drive fails you lose your video. It's not for me to say if this is acceptable or not because it depends on your situation. However, 3TB is a lot of video to lose by anyone's standards. Also, if a drive fails, typically it is not field replaceable and so you have to send the entire unit back for repair, including your sensitive video. At this point you can no longer control who watches the video and you have to rely on service professionalism and good faith.

An option is to configure the hard drives as a RAID - Redundant Array of Independent Disks, which immediately improves reliability because it can survive one drive failing. There are subtle differences between the most common RAID levels in CCTV, RAID, 4, 5 and 6, but the most common is RAID 5 and they all provide protection in case of a disk failure. If a drive fails, you don't even power down the machine - you just eject the faulty drive and insert a new one. After a few hours of the disk array rebuilding itself you are back to normal.

Currently DVRs rarely support RAID inside the box - it is far more common to attach an external disk array to a DVR (using a SCSI cable), and barely use the DVR's internal HDD. These off-the-shelf disk arrays are always more expensive, and noisy, than internal hard drives, but they are more reliable - and you can choose from many different manufacturers with subtly varying features. To achieve economies of scale you can sometimes share one disk array between 2 or even 4 DVRs - assuming the DVRs are co-located and all within a couple of feet from the disk array. Such disk arrays come in different sizes ranging from 2TB to over 10TB.

Disk arrays are often associated with centralized storage, which is why it is the default storage type for IP video where dozens or hundreds of IP cameras' or IP encoders' streams find their way across an IP network to reach an NVR server, and land safely on the directly-attached SCSI disk array. The alternative design is to use iSCSI disk arrays, and stream those same IP cameras and encoders directly to the disk array without going through an NVR - Bosch refers to this as Direct-to-iSCSI and it combines all the reliability and scalability benefits of a RAID disk array, whilst eliminating the need for NVRs, which are expensive bottleneck PCs running operating systems and anti-virus software.

But even with IP video, some people don't use RAID. For example some people use encoders with a small hard drive embedded in the encoder, or a direct-attached USB hard drive, or a removable CF card. Others are using tiny memory cards embedded inside the IP camera itself. These are reminiscent of the concept of a DVR and are completely viable solutions for specific IP video applications, and Bosch refers to this as Recording at the Edge, because the video does not have to traverse the network to get recorded.

I'm not suggesting that everyone buy RAID storage, after all Bosch sells both DVRs with embedded HDDs as well as RAID disk arrays, and as with all things one is not outright better than the other, but for a given situation one is likely to be more appropriate than the other. But I did want to share some of my thoughts, especially with those that could benefit from its value but aren't sure about taking the next step.

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