Lee Middleton, Technical Support Manager at Dedicated Micros, answers your queries on CCTV
What’s the best system for archiving?

Q: With more reasonably priced digital recorders becoming available, could you please explain what are the most common ways of storing images externally and what length of recording will they give me?

A: This is quite a hot topic at the moment because of both the growing popularity of digital solutions, and also the plethora of archiving options available to the installer. My advice is to determine first what your needs are: whether you require Event/Alarm archiving (short video clips) or total archiving (full day and upwards). Second, take into account the rules that determine what length of recording you will achieve, as described in this column in the April issue (“How are digital record times calculated?”) and how much storage this will require. Some of the more popular choices for both short and long term archiving currently include:

High Density Disks – Zip, Jaz etc These devices, capable of storing from 250MB to 2GB of data, are inexpensive and readily available through PC outlets. They are not dissimilar in looks to the floppy used in a standard PC. Although relatively small in terms of data storage, they are ideal for applications where you require short bursts of video archived from your recorder’s hard drive, ie alarm, activity or event clips.

Digital Tape Storage – DDS, VXA etc The CCTV industry has been using this as a storage medium since the very early days of digital recorders. The tapes themselves vary, but on average are about the size of a camcorder tape.

Ideal storage for long term archiving

Certain manufacturers’ devices will allow the storage of more than 30GB of data on a single tape. To put this in perspective, if you were working with an 18KB picture file, 20GB would give you more than 24 hours’ recording at 11 pictures per second. As you can imagine, this makes it an ideal storage medium for long-term library archiving and provides equivalent performance to an S-VHS timelapse VCR.

Most digital recorders are user-definable in the way they archive their data, allowing you to use a tape a day, or for the weekend, in the same way as many conventional analogue systems do.

Hard Drives – RAID devices etc These are really extensions of your internal hard drive. RAID (Redundant Array of Inexpensive Disks) is a device that enables you to stack a number of drives together creating one large hard drive. One of the main benefits is that this enables you to store many days of recording without the need to change tapes or disks.

As an example, if you had a RAID with a total of 200GB, a picture file of 18KB @ 11 pictures per second the total storage capacity would be in excess of ten days.

Being driven by demand in the PC marketplace, the cost of these drives is decreasing while their capacity is increasing, making them a very cost-effective device for storing images.

DVD Recorders DVD (Digital Versatile Disk) is a relative newcomer to the data storage market. Although it’s a dual-sided disk, at present only single-sided recorders are available. Physically, it is identical to a standard CD-ROM but has a far greater storage capacity, of up to 2.6GB.

On its own it is ideal for event/alarm recording, but if you combine the writer with an auto disk feeder it turns it into a type of jukebox (some auto holders can hold in excess of 100 disks), thus giving you a very large recording medium.