The Case for RAID for Video Surveillance
Recording a lot of digital surveillance video, can make a hard drive essential for storage. Unfortunately, with any hard drive, there is a high risk of failure. Hard disks are also a bottle neck in terms of system performance. This is where Redundant Array of Independent Disks, otherwise known as RAID, comes into the picture.
RAID is a method of combining hard disks to achieve redundancy, greater speed or both. People most commonly use RAID for security surveillance applications.
RAID comes in levels 0-6. The most common RAID levels used in security surveillance are 5 and 6.
RAID 0 is all about increasing speed only and offers no redundancy. Level 0 consists of striping without mirroring or parity and allows a group of hard drives to act as a single usable storage array with increased performance of distributing load across all hard drives.
RAID 1 mirrors all data to two or more drives without parity or striping. Multiple pairs of mirrored hard drives can be striped together in a RAID 10 or a RAID 1+0 array. This is the most fault tolerant RAID setup since all data is mirrored fully, however since it requires twice as many hard drives to provide the needed capacity, it’s typically used only for operating systems or programs. RAID 1 is rarely used for storing large amounts of surveillance video.
RAID 5 and 6
RAID 5 and 6 are commonly used to store large amounts of surveillance video.
RAID 5 is composed of three or more disks that provide redundancy and increase speed. RAID 5 allows you to fault one disk. What this means is when you lose a drive, your system will still run. When you replace the drive, the data will be rebuilt with the information that was on the missing drive. It should be noted that when a hard drive is replaced, the system may still be vulnerable to data loss because it takes time to rebuild the entire data volume that was lost. Also, the system is unable to generate new parity data until the data on the hard drive has been rebuilt.
For extra redundancy, people will switch to RAID 6. It is similar to RAID 5 except that it can fault two drives.
Avigilon’s HD-NVR servers are configured with RAID 5 redundancy across the six hard drives installed, while Avigilon Expansion units are configured with RAID 6. Avigilon Control Center software will work on all RAID levels, provided the system can maintain the required performance.
The Truth about RAID
A common misconception people have about RAID is that is it foolproof. Unfortunately, that is not the case as it’s possible for multiple disks to fail. This can happen all at once or over time. If an administrator isn’t properly monitoring the server for disk failures, disks can fail over time causing the array to fail.
The more disks that you have in your array, the higher probability of failure. While RAID 5 and RAID 6 do offer some comfort in protecting your data, it is highly recommended that people also back up their data, especially if it is critical. Don’t assume having RAID is good enough.
What RAID Level Should I Use?
Whether you choose to implement RAID depends on the answers to the following questions:
- Do I need to have redundancy and/or high disk speed access?
- Is this data critical and needs to be available at all times?
If you say no, then single drive is all you need. You get more storage for the same price because all of your space will be realized. However, if you answered yes and the data you need is critical, then using RAID with a backup is one recommendation.
For critical data, some may choose one or more of these options:
1. Record (multicast) to two servers that are in a RAID simultaneously. If something goes wrong with one server, the other will have the data intact and will be recording.
2. Bump the RAID level to 6 or a combination of different RAID levels. With a RAID 6, you increase the redundancy factor and can have two disks fail, but here is also the speed factor because it writes data to multiple disks at once. Be aware - RAID 6 takes up more space compared to RAID 5, so there is a trade-off of losing space, but increasing your security.
Leveraging RAID offers a) some peace of mind that if your drive dies in your system, it will just keep running and b) you get a speed increase which allows you to run your video application successfully.
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