Advantages of RAID6 over RAID5 For Video Surveillance

By: Carl Lindgren, Published on Apr 15, 2009

For large scale video surveillance deployments, like casinos, the enhanced redundancy provided in RAID6 over  RAID5 is critical to minimizing video loss and ensuring system performance. [Note: If you are not familiar with RAID, view a RAID tutorial and a general comparison between RAID5 and RAID6 [link no longer available]]

Background

We have been recording all of our cameras using an NVR system since late 2003.  Our original system consisted of 28 servers, each recording up to 32 cameras.  The servers originally used 16-bay RAIDs with 250GB drives in a RAID 5 configuration.  The majority of the RAIDs were SCSI/PATA, which means they used standard IDE desktop drives in the RAID enclosure.  These drives were not designed to handle continuous video recording and began to fail at an alarming rate within a year.  Our drive vendor replaced these with RAID Edition drives in early 2005, which resolved some of the issues.  At the time, we had a bit over 830 drives in use.

Drive Failures

Even after replacing all 830 drives, we still experienced drive failures.  This is normal for any large system.  It has been estimated that approximately 1% of installed hard drives will fail in the first year of operation; with that rate climbing as the drives age.  There are many possible ways for hard drives to fail and RAID systems can recover from most failures by rebuilding the RAID system using the parity information that is striped across the drives.

RAID 5 uses one parity stripe to store data that can be used to reconstruct the contents of a failed drive onto a replacement drive.  That is the reason why most RAID manufacturers recommend installing at least one global hot spare in each RAID chassis.  When a RAID encounters an error with a hard drive, it “rebuilds” the data that was on the failed drive onto the spare using the parity data.  The failed drive can then be replaced with a new drive; which is designated as the new hot spare.  This process can be done over and over as drives fail and theoretically will keep the RAID storage operating continuously with no data lost.

Unfortunately, there are drive failure scenarios that can not be accommodated by most RAID storage systems that are used for recording video.  This issue is unique to video recording and seldom surfaces in RAID systems used by other applications.  The key is that for most applications, written data is “verified” during the write process.  This means that after a piece of data is written, it is read and compared to the original data before the next piece is written.  If the compare process fails, the area of the disk that failed is marked bad by the drive and the data is re-written to another area of the disk reserved for that purpose.

This process works well when the system has the time to verify the write and repair any errors encountered.  For most applications, there is no requirement to write data continuously and the computer’s operating system can wait the relatively short period required to verify each write and relocate data if an error is encountered.

Video recording is a completely different animal.  It has been estimated that CCTV video recording is 90% write versus 10% read.  I am of the opinion that is a conservative estimate.  An analysis of our system leads me to estimate that the percentages are somewhere between 99% to 1% and 99.9% to 0.01%.  RAID systems set up for video recording seldom, if ever, are set up to verify the data as it is written.

This sets up a possibly fatal scenario.  One of the failure modes of computer hard drives is something called “Read Element Failure”.  The best definition I can find of that is the drive is unable to read all or part of the data written to it.  This could be the result of a complete failure of one of the read heads, or just a bad area of a disk that has not been relocated by the drive’s automatic systems.

Get Notified of Video Surveillance Breaking News
Get Notified of Video Surveillance Breaking News

Since the drives in a video recording system don’t normally automatically read the data after it is written and the system operators only play back a very small fraction of the video being recorded, a drive could happily chug along writing data that is unreadable for a long time.  Neither the system nor the operators would ever know that there is a problem.  That is, until a drive fails with a problem that is recognized by the RAID system.

When the RAID system encounters a drive failure that it recognizes, it will attempt to rebuild the RAID set using the parity data recorded across all of the drives.  That is where the problem becomes acute.  If the RAID system also contains a drive that has a Read Element Failure, it is very possible that bad area contains parity data.  If it does, the rebuild will fail.

On a RAID 5 system, if a rebuild fails because the parity data is corrupt or unreadable, the system now has two bad drives and the RAID set is lost.  This happened to us at least six times during the three years that we used our original RAID 5 systems.

RAID 6

RAID 6 works a bit differently than RAID 5.  Although it can encounter the same drive failure scenarios as RAID 5, its ability to recover from them is greatly enhanced by the method RAID 6 records the parity data.  Instead of writing one parity stripe across all drives in a RAID set, RAID 6 writes two completely independent parity stripes.  There are two advantages to this: RAID 6 is able to recover from the simultaneous failure of two drives in the enclosure and its two parity stripes are in different areas, allowing the system to read parity even through multiple failures.;

This has been proven by us in our recording environment.  In 2006, we replaced all of our servers and RAIDs.  Our new RAIDs were set up, at our insistence, as RAID 6.  Although we have experienced at least three instances where two drives failed in an enclosure, including at least two instances where the second drive failed during the rebuild process, we have never lost any data.  The systems rebuilt both failed drives and continued to run flawlessly.

Conclusion

For these reasons, I would never recommend using RAID 5 in a critical video recording environment.  The risks of data loss are too great.

 

1 report cite this report:

How Costly are Hard Drive Failures? on Apr 29, 2009
Storage tends to be one of the more costly and problematic parts of video...

Related Reports

Vulnerability Directory For Access Credentials on Feb 20, 2020
Knowing which access credentials are insecure can be difficult to see,...
Uniview Deep Learning Camera Tested on Jul 14, 2020
Uniview's intrusion analytics have performed poorly in our shootouts. Now,...
Video Analytics 101 on Mar 16, 2020
This guide teaches the fundamentals of video surveillance...
Milestone Presents XProtect On AWS on May 04, 2020
Milestone presented its XProtect on AWS offering at the April 2020 IPVM New...
Remote Network Access for Video Surveillance Guide on Jul 27, 2020
Remotely accessing surveillance systems is key in 2020, with more and more...
ROG Security - Cloud AI For Remote Monitoring on Jan 28, 2020
ROG Security is offering cloud-based AI analytics to remote guard companies,...
VSaaS Online Show June 2020 - On-Demand Recording of 25+ Manufacturers Presentations on Jun 24, 2020
The show featured 25+ VSaaS providers showcasing their latest services. The...
NetApp Presents Hybrid Cloud Video Archive on May 11, 2020
NetApp presented its hybrid S3 cloud video archive at the April 2020 IPVM New...
Video Surveillance History on May 06, 2020
The video surveillance market has changed significantly since 2000, going...
Vehicle Gate Access Control Guide on Mar 19, 2020
Vehicle gate access control demands integrating various systems to keep...
Breaking Into A Facility Using Canned Air Tested on Jan 28, 2020
Access control is supposed to make doors more secure, but a $5 can of...
TVT / InVid Facial Recognition Tested on Mar 25, 2020
Facial recognition is frequently sold for thousands of dollars per channel...
Fever Camera Sales From Integrators Surveyed on Jun 01, 2020
Fever cameras are the hottest trend in video surveillance currently but how...
Integrated IR Camera Shootout 2020 - Avigilon, Axis, Bosch, Dahua, Hanwha, Hikvision, Panasonic, Uniview, Vivotek on Jan 30, 2020
The best and worst cameras tested in this IPVM shootout showed major...
Vivotek LPR Camera Tested on Apr 15, 2020
Vivotek has historically sold license plate capture cameras but not LPR. Now,...

Recent Reports

Google Invests in ADT, ADT Stock Soars on Aug 03, 2020
Google has announced a $450 million investment in the Florida-based security...
US Startup Fever Inspect Examined on Aug 03, 2020
Undoubtedly late to fever cameras, this US company, Fever Inspect, led by a...
Motorola Solutions Acquires Pelco on Aug 03, 2020
Motorola Solutions has acquired Pelco, pledging to bring blue back and make...
False: Verkada: "If You Want To Remote View Your Cameras You Need To Punch Holes In Your Firewall" on Jul 31, 2020
Verkada falsely declared to “3,000+ customers”, “300 school districts”, and...
US GSA Explains NDAA 889 Part B Blacklisting on Jul 31, 2020
With the 'Blacklist Clause' going into effect August 13 that bans the US...
Access Control Online Show July 2020 - On-Demand Recording of 45+ Manufacturers Presentations on Jul 30, 2020
The show featured 48 Access Control presentations, all now recorded and...
Face Detection Shootout - Dahua, Hanwha, Hikvision, Uniview, Vivotek on Jul 30, 2020
Face detection analytics are available from a number of manufactures...
Sunell is The First China Manufacturer to Market NDAA Compliance on Jul 30, 2020
Most China manufacturers are going to be impacted by the NDAA 'Blacklist...
Ink Labs Relabels China YCX Fever Camera And Steals Dahua's Marketing on Jul 30, 2020
A US company marketed a 'thermal temperature scanner' as its own, selling...
Genetec and Dahua-Backed Intelbras Split Examined on Jul 29, 2020
China is the cause of the breakup between Canada's and Brazil's largest video...
This YouTuber is Now Selling ThermoHealth Temperature Screening on Jul 29, 2020
An enterprising 20-year old is mass marketing medical devices on Facebook and...
Hikvision Returns To Growth Driven By Overseas Fever Cameras on Jul 29, 2020
While Hikvision's revenue fell in Q1 2020, it rebounded in Q2 attributed to...
Brazil's Biggest Domestic Surveillance Company Intelbras Profile on Jul 29, 2020
While Intelbras is not widely known outside of Latin America, Intelbras is a...
The Kiosk Market Pivots To Temperature Screening (Interviewed) on Jul 28, 2020
Video surveillance is not the only market that has pivoted to medical device...
Integrator Acquisitions 'A Good Market' During COVID-19, Says Greybeards on Jul 28, 2020
Industry broker Ron Davis of the "Greybeards" says that the integrator and...