CCTV devices record and save compressed audio and video in a digital format, which provides a host of opportunities in terms of processing and transmission. The most commonly employed solutions include:
- independent DVRs or NVRs,
- PCs with NVR software,
- NAS and SAN drives,
- FTP servers,
- backup/independent camera recorders.
The bulk of CCTV systems rely on HDDs. Semiconductor drives, such as SSDs, are not commonly used due to their fallibility and higher cost. In CCTV systems, image streams are recorded in a loop and data is frequently overwritten, which means that HDDs offer a significant advantage.
A hard drive a key element of any CCTV system. Its parameters are crucial for the quality and reliability of camera video recording. HDDs employed for monitoring purposes, however, work under conditions different than those used in PCs. In CCTV systems, data is recorded on a continuous basis and accounts for more than 90% of the disk load. Another great challenge is the need to simultaneously handle multiple data streams generated by individual cameras. PC hard drives are not only more fallible, but also fail to ensure the adequate performance to handle multiple cameras in CCTV environments. Below, we compare the main features of the above two types of hard drives.
- are designed to read and write small data blocks and handle random transfers of up to 60 TB/year,
- have a working time limited to 8 hours per day, 5 days a week,
- are not designed to handle multiple cameras,
- don't have rotational motion sensors or the RAID function, which are required in multiple-disk systems,
- don't have power management functions and cannot work in high heat conditions.
In contrast to PC drives, Seagate's SkyHawk HDDs
are optimized to work with CCTV systems. They:
- are designed to support 24/7 surveillance workloads all year round,
- have a workload rate limit of up to 550 TB/year,
spend 90% of the time taking in streams, with the remaining 10% dedicated to playback,
- support footage from multiple cameras without the risk of losing image frames,
- ensure reliability, vibration resistance, and high performance in multiple-disk systems,
- have advanced power management functions,
come with a built-in SkyHawk Health Management software that actively protects surveillance storage by focusing on prevention, intervention, and recovery options.
Hard drives used in CCTV systems are exposed to intense vibrations, which may cause data recording or playback problems. Particularly at risk are those installed in multi-drive DVRs/NVRs and devices equipped with forced-air fan cooling systems. Vibrations generated by neighboring drives and fans reduce the overall performance of the data recording system, and if they are intense enough, they may even cause damage to the actuator of the read/write arm.
VCM and PZT actuators on the read/write arm
HDDs are designed to ensure adequate system performance even in the face of vibrations. The read/write arm is controlled by two systems. The (standard) VCM actuator controls its quick movements on the platter (for the purposes of data writing and reading), while the (sonic) PZT micro-actuator additionally compensates any vibrations. Both actuators are activated by a special controller that operates in a feedback loop, which analyzes the vibrations of the two rotational vibration (RV) sensors on the control board. Maintaining proper control of the two actuators allows to balance out the vibrations of the write/read arm.
The rotational vibration sensors, controllers operating in a feedback loop and PZT micro actuator (A)
ensure effective vibration compensation
Using "regular" HDDs in CCTV systems involves the risk of data loss. The problem is due to the fact that the HDDs employed for monitoring purposes work under conditions different than those used in PCs. In CCTV systems, data is recorded on a continuous basis and accounts for more than 90% of the disk load. Another great challenge is the need to simultaneously handle multiple data streams generated by individual cameras.
The algorithm that governs cache data storage and what happens when the buffer is full
CCTV drives are controlled by a dedicated firmware, based on multi-tier caching (MTC) technology, which guarantees high image integrity and the simultaneous recording of video streams from up to 64 cameras. The ATA-8 protocol is optimized to handle sequences of large data blocks. Data from the DVRs/NVRs are stored in the disk buffer and only copied to non-volatile memory when the cache is full. This method reduces the number of necessary read/write operations, which translates into greater reliability.
Large cache memory allows to limit the number of write operations
In order to be efficient, large file transfers require not only considerable throughput, but also the availability of error-correction functions that help preserve data coherence during transmission. SkyHawk HDDs rely on a special data correction algorithm that reduces the loss of image frames during write operations. The firmware of the HDD cooperates with the DVR/NVR to ensure the appropriate query handling time, thus minimizing the risk of DVR/NVR buffer overflow and preventing the loss of image frames during playback.
SkyHawk HDDs guarantee very long failure-free operating periods. Suffice it to mention that HDDs with the ImagePerfect firmware typically achieve an MTBF of 1.5 million hours on average. When used for the 24/7 recording of video streams from 16 cameras, they can thus be expected to operate reliably for more than 11 years.
SkyHawk Health Management (SHM) is an embedded software designed to notify the user of any actions that could adversely affect HDD health. SHM monitors HDD parameters and operating conditions (such as temperature, humidity, vibrations) and may recommend a specific action (e.g. a reduction in the temperature or the number of HDDs) if it identifies a risk to HDD health. If the condition of the HDD is compromised, the system will automatically recommend its backup to ensure continued data access.
View of the SkyHawk Health Management window, available in the NVR menu
View of a warning message
View of a warning message
RAID Rapid Rebuild is the latest function designed to reduce the time needed to perform volume rebuilds. It rebuilds only the failed striped data, then copies over the rest of the unaffected data to a spare hard drive. The SHM system is integrated with 4 TB SkyHawk HDDs and compatible with Hikvision NVRs (v4.X).