The expansion of megapixel and HD cameras in the market requires extra storage. But where do DVRs and NVRs back up data? Attached storage devices are the answer, freeing up recorder space while keeping footage indefinitely.
Megapixel and HD cameras are at the forefront of security trends. Compared to SD cameras, they create larger files that cannot be absorbed by current storage devices. These cameras are mostly implemented in sensitive areas, such as airports. Government The expansion of megapixel and HD cameras in the market requires extra storage. But where do DVRs and NVRs back up data? Attached storage devices are the answer, freeing up recorder space while keeping footage indefinitely. Laws often mandate related video to be stored for a period of one to six months for security and evidence purposes.
Storage devices such as DVRs or NVRs cannot store footage indefinitely, due to limited capacity. Onboard drives are routinely wiped to free up memory, which may be before the device has stored one to six months of footage. To get the data off the device and comply with mandates, extended storage devices serve as backup memory.
There are many storage options available, and it is difficult to determine which type of extended storage is needed without considering the project. "Attention should be given to the three main attributes of networked storage — scalability, availability and manageability — and an assessment made as to how important each is to the project's overall goals," said Clifford Cox, Product Manager of Digital Video Systems, UTC Fire & Security. "Performance, cost and operation are the three key challenges that must then be managed."
The amount of storage needed shifts based on the camera and video compression used. "The typical amount of storage required per camera is high. The amount of storage varies depending on the resolution of the camera, data compression used, frame rate, hours of camera use, percentage of motion detected and the number of required storage days. You can range from 50 to 270 gigabytes per camera depending on the resolution, compression, bit rate and so on," said Bob Mesnik, President of Kintronics.
The longer data is stored, the more storage is needed. This is because all incoming data is kept instead of being overwritten. "A bank with sixteen 1.3-megapixel cameras using H.264 compression would take up 180 terabytes, if the data is stored for half a year," said Andrew Yu, Product Manager of Surveillance Business Division, QNAP Systems.
For the convenience of buyers, many companies supply online calculators to help specify their storage needs. For smaller files, a USB drive can be sufficient for storing data. With larger files, a network-attached storage (NAS) or storage area network (SAN) device will be required.
USB and Optical Disks
USB drives and DVDs are convenient for storing data, since saving data for extended periods of time is often costly and unnecessary, unless required by law. When the DVR or NVR reaches its storage capacity, data can be transferred to USB drives or optical storage. "A blank USB drive can be inserted into the NVR to retrieve the data for storage," Yu said. Then, it is simply tucked away in storage until the data can be discarded. This option is the simplest and most budget-friendly for many users, who do not need to set up a storage network or have smaller budgets.
Currently, the most common extended storage media is direct attached storage (DAS). "Most DVRs and NVRs are designed to use DAS, but these devices lack the ability for the high performance data transmission necessary for networked storage," Cox said. They are, however, cheaper, and compatible with most existing DVRs and NVRs.
The DAS is linked to a single DVR or NVR, without a network in between. "Disks are directly attached to the motherboard, and through that, to the CPUs in the system," said Jeff Whitney, VP of Marketing, Intransa. "It is the simplest of storage infrastructures, but is limited in capacity, performance and reliability."
When many cameras are used or image files are bigger, more DVRs, NVRs and DAS devices are needed. This could increase long-term costs, as well as increase the physical space needed for the equipment. "Small deployments with low storage requirements traditionally utilize DAS, while larger deployments may leverage DAS in a mixed storage environment that likely includes NAS and/or SAN," said Steven Kappel, GM of Security and Fire for the Mid-Atlantic Region, Johnson Controls.
DAS is recommended for smaller installations. "External DAS is best used when the capacity requirements are well known, will not expand over time and where the performance requirements are fixed," said Lee Caswell, founder and CMO of Pivot3.
JBOD and RAID 0
Another affordable option for extended storage can be found in JBOD. "JBOD is an acronym for 'just a bunch of disks,' and is typically used today as low-cost storage that can be plugged into a DVR or a video appliance solution," Whitney said.
A redundant array of independent disks (RAID) at level 0 is similar to
JBOD, but it uses a different method for storing data to a system. With JBOD, the data is filed in order, from one disk to the next when a disk reaches full capacity. The RAID 0, however, saves all incoming data randomly onto a minimum of two disks at the same time, which increases performance significantly. They can both be used independently or within a NAS or a SAN system.
Files can be stored and shared on existing network infrastructure using a NAS unit, said Trenton Baker, Marketing Manager at Aberdeen. They are more affordable and sufficient for mid-range projects. Unlike conventional servers, NAS storage uses performance-optimized components, such as faster RAID controllers and hard drives.
Network storage enables more users to access data. "Local files are managed by the NAS device, which has its own IP address accessible to other IP devices on the local area network (LAN)," said David Burks, Director of Global Marketing, Desktop, Consumer Electronics and Video Surveillance Markets, Seagate Technology.
Thus, it is convenient for users to back up data from an NVR to a remote NAS, Yu said.
Sharing security image files is rare and having a NAS unit does not mean it is used for data sharing alone. "A NAS with iSCSI service can be partly dedicated to file sharing and also remotely store data at the same time," said Jerome Jaussaud, Product Manager, Product Management Department, Sales and Marketing, QNAP Systems.
NAS offers advantages for surveillance applications. "The file system on the NAS platform is easier to support a hybrid storage case, where some storage occurs locally on self-contained NVR and DVRs, and extended storage is sent to a specific file on the NAS," Caswell said. "But there is a performance tradeoff because it is much more complex to share and send file-based data versus the raw blocks on the SAN."
However, the file-based nature of NAS systems make them problematic for high density and high bandwidth video storage, Cox said. This requires careful attention to the server and the network loads when considering NAS.
NAS is less suited for large projects with many megapixel or HD cameras. "As a result, NAS products are often used in more lightly loaded distributed environments," said Caswell.
A SAN is most suited for storing large image files from megapixel and HD cameras. A NAS system focuses on file sharing and simply storing data, whereas the SAN focus on high performance. "SAN management is typically complex and requires specialized training and software," Burks said. "Data is transferred at the disk block level instead of the file level."
Blocks are the native IP protocol for transporting video data. "In terms of streaming video, SANs are an ideal selection, which does not interject an additional operating system like NAS does," Whitney said.
Unlike the NAS, the SAN can store images remotely. "SAN systems are networks of storage devices that could include servers and digital tape libraries that may be remotely located, but can be accessed as if they are locally attached," said Mark Wilson, VP of Marketing, Infinova.
Additional SAN units can be added as storage needs increase, which makes expansion easy. "It is not easy to predict how much data is generated by individual cameras since bit rates are dependent on assumptions on how much motion will be detected," Caswell said. "The amount of motion can dramatically affect the amount of data needs and what the configuration should be."
Two common transmission protocols are iSCSI for IP SAN and fiber channel for fiber channel SAN. "Fiber channel SAN is more reliable and can be used to build a larger and more flexible storage network, but include proprietary fiber channel host bus adapters," Baker said. "Switch and channel requirements make it an expensive option."
Despite the price, some applications require speedy high-performance video, particularly large corporations and government projects. "The file transfer speed per 8-gigabyte fiber channel port is around 600 gigabyte per second," Baker said. "It is seven to 12 times faster compared to the NAS, and around six times faster than a 1-gigabyte iSCSI SAN connection." However, expanding fiber channel projects can raise costs significantly.
IP SAN connects through a wireless network or Ethernet channels. "All SANs before were connected via fiber channel, which can be expensive, but now, there is IP SAN which is more affordable," Jaussaud said.
Compared to fiber channel SAN, IP SAN can be implemented on a smaller budget. "Most of the storage related features can be achieved using IP SAN on the existing network infrastructure, cabling and hardware in a more limited distance," Baker said. The only downside to using IP SAN is that extended distances can affect data transmission for storage.
The distance from the NVR to a SAN system can be much greater compared to DAS or NAS systems. This is useful for installations with multiple sites.
RAID 5 and RAID 6
System failures can mean losing critical data. "Storage failures are almost always minimized by the use of RAID, in conjunction with the hot-swap capability of individual storage devices," said Craig Howie, Commercial Director of Visimetrics. "Other forms of data monitoring and integrity include status monitoring of individual storage devices for read errors, over temperature or RAID volume status."
Redundancy is achieved using RAID. "RAID aims at storage reliability and input/output performance," Wilson said. The RAID level depends on the number of hard drives required and their capacity for storage, minus a hard drive used to store parity data.
Common RAID levels for surveillance are RAID 5 and RAID 6, which strip data across multiple hard drives for automated backup and redundancy. "If a drive in a RAID system fails, the content can be rebuilt from the other drives in the RAID system," Burk said.
A RAID unit is capable of protecting up to 100 drives. "RAID 5 is commonly used in storage systems of two to 80 terabytes for recording video," Whitney said. "The system can keep running during the rebuilding process, which is important for nonstop video surveillance environments."
As soon a hard drive fails, a notification is sent and sufficient time is provided for a new hard drive to be inserted. RAID 6 works in the same way, except with two sets of parity data to accommodate two hard drive failures. This increases the minimum number of hard drives needed. RAID 5 requires a minimum of three drives, while RAID 6 requires four. Only units with three or more hard drives are capable of sparing one for parity data, which means RAID 0 and JBOD devices are not protected against data loss.
Aside from providing redundancy, data is stored faster, since it is distributed and written on separate drives simultaneously. "Increased speed of data storage is important because data could constantly be transferred from the NVR to the RAID unit when large image files are constantly streaming in," Mesnik said.
Mirroring is when a spare hard drive is used for a backup copy as opposed to many, like in a RAID device. "Because mirroring uses a single hard drive for backup, it can be slower in comparison," Wilson said.
RAID 1 mirroring is when the same data file is being written on two different hard drives in real time, but it is not sufficient for data protection. "It is not as popular anymore, and can mostly be found in 30 percent of higher-quality NVRs, as opposed to extended storage devices," said Jack Yang, Senior Manager, Product Planning and Marketing, Promise Technology.
Hard drives are categorized into fiber channel, SCSI, SATA and SAS. Fiber channel and SCSI hard drives are used for enterprise purposes, which makes them expensive. "Fiber channel and SCSI hard drives are also out of date, even though they cost twice as much as a SATA drive. They have better drive performance speeds at 15,000 rpm, but it is too much for surveillance and their capacity is too small," Yang said. "SAS may have higher performance and dual paths for redundancy, but it becomes too expensive to be used in surveillance, which is why SATA drives are the best choice."
SATA drives are categorized by different levels of quality, with enterprise SATA drives considered to be most favorable. "AV and surveillance SATA drives are used for DVRs and NVRs as internal disks, so vibration is not too much of an issue," Yang said. "But when used in a RAID device, it lacks vibration correction and the failure rate is high, which means maintenance and replacement costs are high."
Specifying different hard drives is important because storage devices do not support all drives. Most devices support SATA and SAS drives, but some can only support SATA drives. Hard drive requirements needed to prevent selecting incompatible storage devices should be seriously considered.