Most Video Storage solutions available today are based on solutions prevalent in the I.T. domain. With the transition of Video surveillance to IP, it was quite natural to use available I.T. storage solutions. However these storage products were designed for the enterprise IT market, for applications like DB, file and print, email etc.
Video Storage requirements are in direct contrast to traditional IT storage I.T. Storage
• Traffic patterns are diverse from small to large files.
• More read versus write – usually 70% read versus 30% write
• Has various sequential and random patterns.
• Files are generally small and hence the hard disks are formatted into smaller blocks – typically 4 KB.
Video Surveillance Data
• It is primarily ‘write traffic’ – more than 95% of the times.
• Each video stream is sequential in nature and written to files that are generally large – typically 64 KB Video stream is sequential in nature and written to files that are generally large and hence the disks are formatted into large blocks – typically 64 KB.
Significance of sequential nature and file size of Video streams
When using I.T. Storage, as the total number of camera video streams grows, each file is written to a different physical location on the disks. As a result:
• The disk heads needs to jump around to write to all the files concurrently.
• The combined pattern becomes random even though each camera’s video stream is sequential in nature.
The typical, general-purpose storage system performs poorly in this multicamera video stream environment. It also becomes difficult to scale up with more cameras, higher resolution cameras and longer retention periods. This demand results in high-cost-per-camera video streams.
For video traffic, the key question is whether the video frames are saved into the storage system. In an IT environment, if the storage system takes a long time to write something to a disk, the storage system can signal a “please wait” all the way back to the desktop computer that issued the write, and the person simply waits a few seconds longer for the data to be written to the storage product. In the video-surveillance environment, data is written to disk from a camera.The cameras will output video frames at up to 30 frames per second. If the storage cannot write the video to disk fast enough, video frames will be dropped.
IT storage features that Video doesn’t need
Several IT storage features such as snapshot, replication, continuous data availability, thin provisioning, 8k fixed de-duplication for block and file and single instance deduplication for file, block and file compress are not required for Video storage and are actually counter intuitive to good video surveillance storage.
Snapshot would only be needed when data needs to be overwritten constantly (such as in a database). You don’t want to back up data while it is changing, so you take a snapshot first. For surveillance, we only archive the data recorded hours, days or weeks ago. The data does not change. It is static. No snapshot is needed! Replication is actually intended only for database.
The replication could be “synchronous” or “asynchronous” for each IO command. This granularity ensures the correctness for each IO command across geographical locations. This is not easy to do. If the system loses synchronization between two sites due to network problems, it will need to re-sync before moving forward. Video surveillance does not need per command data coherency. One can easily archive recorded data to
a remote site without this level of synchronization.
Anything regarding duplication and compression is actually not required for video surveillanc storage. IP cameras have already compressed video using H.264 Computing and metadata management just wastes storage resources. 8K block is for database. Video surveillance only uses large blocks such as 64KB or higher. Thin provisioning is also only for IT. There is no thin provisioning in surveillance. The video retention period – number of days or months is
• Video storage has very specific needs.
• Video surveillance storage solution should be equipped with a write focus, large blocks for video streams, the ability
to ensure that video frames are never dropped and much more.
• Traditional IT storage solutions might have an abundance of impressive features like replication and duplication, but they are not needed for video storage.
• The end user needs storage that is built for video surveillance.
Kiron Kunte has over 35 years of design and solutions experience, in Security, Telephony and Networking infrastructure. He is a graduate of IIT Bombay, a Fellow of the Institute of Engineers and has a post-graduate diploma, from Bombay University, in Systems Management. He is professionally certified in the design and engineering of Data Centres, IP Telephony, Video surveillance and Structured Cabling solutions. He heads Norik Konsult, a practice that offers advisory, design and system planning help to upgrade or build a new Telephony, Security and Networking infrastructure.
For more information contact: www.norikkonsult.com