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Ask the Expert: What are the options for adding more storage to a CCTV system?

On a very basic level, if the system uses an embedded DVR, you may have the option to add storage capacity to the device. For example, some DVRs that use RAID (Redundant Array of Independent Disk) technology allow you to simply add drives or larger-capacity disks when needed.

For systems that record to a directly-attached or remote RAID — the most popular high-capacity digital video storage format — there are two options for expanding storage. With the first, called horizontal storage, you simply attach a new disk array to the network switch and format it to record certain video streams. With this approach each disk array is separate, so you will need to manage multiple RAIDs.

Alternatively, you can increase the capacity of the existing disk array by adding simpler RAIDs, called shelves, to the base unit, as long as the base unit is powerful enough to accommodate this. The advantage of this method, called verticalized storage, is that the daisy-chained RAIDs act as one device — a storage stack. You get the extra capacity you need but can monitor and manage the stack as a single system that requires only one IP address.

If you need to add storage to a large system, you should seriously consider verticalized storage. Working with one unit, or stack, versus multiple separate RAIDs allows for easier system management overall.

There is a disadvantage to verticalized storage, since you have all of your eggs in one basket. If the base unit fails, you lose access to the video recorded on all of the disk arrays. However, you can mitigate this risk by planning for redundancy in the system design — including redundant power supplies, redundant connections from the base unit to the storage shelves, redundant disk controllers and redundant fans. The largest and most critical systems in the world use these techniques to implement massive, yet manageable and reliable, storage area networks.

Also critically important is redundancy at the drive level. A typical RAID device has a number of hard drives and, depending on the configuration, can be set up to use sharing or data replication to deliver higher data integrity and fault tolerance. For example, RAID 5 uses one hard drive to record redundant data so that any hard drive can fail without loss of data. However, a second hard drive failure at this stage results in total loss of video.

For greater reliability, RAID-DP (double parity) technology stores redundant information across all drives and provides over 3,800 times more resiliency than RAID-5 for uninterrupted system functionality. With the parity information, you can automatically recreate missing data even in the event of double disk failures. This level of safeguarding data may be important for expanding storage capacity of the most demanding surveillance applications.

While each approach to expanding storage capacity has its advantages and drawbacks, the growing array of solutions available today gives you several options for system design. The best choice is dependent upon your customers’ specific requirements.

Norm Hoefler is responsible for the Canadian operations for Bosch Security Systems, Inc.
He has worked in the security industry for 17 years in integration, business development and manufacturing.