Bigger Is Better? IP Storage Issues
With many users now requiring security video recordings for 90+ days, the focus has been placed on the storage costs of IP video systems. But with the very best compression technology and the right storage architecture, IP video systems can easily accommodate this requirement.
Many organizations are now requiring that security video images are recorded and archived continuously from all cameras for 90 days or more. In large systems, this can create a significant storage requirement. This is compounded by users wanting to store video at the highest quality and maximum frame rate, particularly in homeland security and law enforcement applications where security video footage is required for evidential purposes. The storage element of a large IP security video system can therefore dominate the overall cost of the system, both upfront costs and lifecycle costs, as hard drives will often need to be replaced over the life of the project.
With potentially large amounts of data being stored, the technology behind the compression employed and the architecture of the storage solution are critical to ensure these extended recording times can be accommodated. Similarly, the security of the stored data is important so that individual disk and equipment failures do not result in data loss.
The Scale of the Problem
The factors that affect how much disk storage is required are video resolution, frame-rate, number of cameras and the quality of the compression technology deployed. So when comparing systems, the main variable is the compression technology, as all other factors are constant. The way in which video is compressed can make a significant difference to the storage requirements.
When it comes to storage, security video systems are very different to IT systems. The amount of data coming from the cameras to the NVRs is huge and continuous. The amount of data coming from the NVR to the users is very low and periodic. The workload is constant, i.e. the rate of writing data to the disk is constantly high, not in bursts as with typical IT applications.
The processing overhead for writing and reading the video streams to disk is therefore an important factor in the overall performance of the NVR. There can be a considerable difference in this overhead between different vendors of NVR software. Software that can minimize this processing will be able to handle many more camera streams per NVR. Therefore, in a large system with a 90-day recording requirement, the limitation on the server is its storage, not its processing power.
The storage architecture for security video systems can be typically categorized as either centralized or distributed.
Centralized Storage Architectures
A typical example of such a system would be a casino, where a high density of cameras are located in one building. The NVRs would be located in one central IT facility, with a central network switch. In this situation, all of the video could be recorded on one server; however, this would almost certainly be storage limited.
Using the worked example above with a 100 camera system, one option would be to use 10 NVR servers, each fitted with an 18 terabyte disk array, assuming the system has the best compression technology available. This is still a lot of hardware, but because the storage utilization is low, virtual servers can be deployed. In reality, the typical casino uses between 500 and 1,000 cameras, so this approach is an important factor in keeping down costs.
Distributed Storage Architectures
A typical example of such a system would be a rail network that could have 200 cameras located across 25 stations with on average eight cameras per station, with some stations only having four cameras. In this situation, what is needed is a small and flexible storage architecture, which can use the right amount of storage for the right amount of cameras.
With so much valuable data being recorded, it’s important to consider NVR security and reliability. Most computer-based NVR servers will deploy Redundant Array of Independent Drives (RAID) disk arrays. A RAID is an umbrella term for computer data storage schemes that divide and/or replicate data among multiple hard drives. There are different RAID levels, giving different levels of protection. In a RAID 5 configuration, for example, the data is striped across three separate disks. If any disk fails, no data is lost and the computer can continue without interruption.
An IP video system that deploys standalone NVR units should also have a flexible NVR backup strategy. For example, if the system software detects an NVR failure, then recordings can be automatically switched to a backup NVR or distributed among other NVRs in the system. Like RAID configurations in PCs, NVRs can be mirrored, with the same video being recorded on two NVRs simultaneously, providing the highest level of security.
DVR vs. NVR
So far discussed have been the storage issues with IP video systems and NVRs, but what about traditional analog security video systems that use digital video recorders (DVRs)? It is important to differentiate between DVRs and NVRs, as both are often termed “digital”. A DVR digitally compresses analog video feeds and stores them on a hard-drive, the term ‘digital’ referring to the compression and storage technology, not the transmitted video images. The DVR has to be located near the analog feeds and is typically only used in centralized architectures. In contrast, an NVR stores digital images directly from the IP-network and can be located anywhere on the network.
It is typical for a DVR to be located centrally, close to the analog matrix and control room equipment. As the size of the system increases and the number of recording days increases there is no other option but to keep adding additional DVRs. This in itself is not a problem other than the cost overhead associated with the DVR. A high-end DVR would typically be able to record 16 cameras on to a 2-terabyte disk. Clearly DVR technology is simply too expensive for large-scale digital recording applications.
Reducing the Amount of Video
There are a number of compression standards currently employed in IP video systems. H.264 is the latest attention-getting video compression standard, which follows on from the highly successful MPEG-2 and MPEG-4 video standards and offers improvements in both video quality and compression. The most significant benefit for IP video systems is the ability to deliver the same high-quality, low latency, digital video with savings of between 25 percent and 50 percent on bandwidth, and therefore on the storage requirements. By selecting a system based on H.264, further savings on storage can be achieved. Even though H.264 is more efficient than MPEG-4, there are still differences between the implementation of the standard and the amount of storage required.
There is no point in recording video from a camera at a full frame rate if there is nothing in the scene to record. By using applications such as activity controlled frame rate, the amount of video and storage can be significantly reduced. When a scene is inactive the video can be streamed at a much lower frame rate. As soon as the motion analysis software detects movement the video is streamed at full frame rate. Similarly analytics such as virtual tripwire can detect an object crossing a line and raise an alarm. This alarm can start recording or increase the frame-rate from that particular camera.
The requirement to record security video images for 90+ days will have a large impact on the storage requirement of the project and the cost. With larger systems, the inflexibility and costs involved with an analog/DVR solution means IP video is the only way forward. It is therefore paramount that security executives choose an IP video solution that can deploy the very best compression technology and flexible and distributed NVR architectures, in order to minimize the additional costs due to the storage overhead.
About the Source
Security Magazine thanks Barry Keepence of Indigo Vision. Before joining that firm as chief technical officer (CTO) in 1999, Barry Keepence worked for over 10 years in the space industry and as a system architect.
SIDEBAR: Virtual Servers
Virtualization is a proven software technology that is rapidly transforming the IT landscape.
Today’s powerful PC hardware was originally designed to run only a single operating system and a single application. Virtualization breaks that bond, making it possible to run multiple operating systems and multiple applications on the same computer at the same time, increasing the utilization and flexibility of hardware.
In essence, virtualization transforms hardware into software. Software such as VMware transforms or “virtualizes” the hardware resources of a PC – including the CPU, RAM, hard disk and network controller – to create a fully functional virtual machine that can run its own operating system and applications just like a “real” computer.
Multiple virtual machines share hardware resources without interfering with each other so that several operating systems and applications can safely be run at the same time on a single computer.
SIDEBAR: Digital Data
The difference between an average compression and the best is 180 Terabytes of extra storage – and that’s just for a relatively small system of 100 cameras.
The amount of digital data generated by a single camera:
Best compression: 20 gigabytes per day
Average compression: 40 gigabytes per day
This does not at first seem unmanageable since hard disk storage is inexpensive and 750 gigabyte disks are readily available. However, assume a system with 100 cameras and the storage changes.
Best compression: 2 terabytes per day
Average compression: 4 terabytes per day
Archiving recordings for 90 days gives:
Best compression: 180 terabytes
Average compression: 360 terabytes