Related: Storage: Redundancy / RAID Statistics.
I added a poll up top about using a dedicated backup device. I think only a minority do because it's expensive and using RAID is typically enough for those who are concerned.
IPVMU Certified | 03/30/14 11:39pm
Thanks for the link to that very interesting article John. It seems ironic to me that customers deem video surveillance important enough to spend a lot of money on hardware and installation but not a little extra to secure the video that has been recorded. For the cost of one decent camera, one could buy a 4TB hard drive to mirror or back up the data from the VMS server.
I'll be interested to find out if anyone here backs up data to another device. From what you've mentioned, this seems unlikely which is a bit scary.
Video surveillance is possibly a unique use case in all the storage realm. So much writing, so little reading. Of course there are particular applications that actually use their data everyday, casinos/large banks cone to mind, and others that need or require long term archival. But for the meat and potatos of cctv from low-end sole prop to the mid-tier warehouse, >99% is just run over without ever reading and even less actually rises to the level of 'vital importance'.
Typical exchange between dealer and small to mid size customer:
Dealer: Yeah, the problem is a drive crapped out. I have a new one with me, its actually way bigger but its the same price.
Customer: Cool, thanks.
Dealer: Was there anything on the bad drive that you needed?
Customer: Wipe it. No harm, no foul.
Although this strategy seems reckless its not quite as bad as it seems since 1. The actual chance of a drive failing that actually has something critical on it is the product of the odds of the drive failing times the odds of something of vital importance happening. So you could easily go your whole life as a customer and never get burned, Murphy nonwithstanding. 2. In my exp. even drives that fail can be recovered, for a price, in 75% of cases.
So in addition to your fine questions, I wonder how many systems have 0% redundancy out there? Tho maybe nobody wants to brag about it. ;)
I wonder how many systems have 0% redundancy out there?
From Storage: Redundancy / RAID Statistics. It's 3 years old and I bet it's improved a little but the bulk of DVR / NVR appliances out there (save NAS ones) are likely to have 0 redundancy.
At least in our case, backing up our streaming recordings would be nearly impossible, but we do backup our evidence clips. Why impossible? We record >1000 cameras at an average bit rate of approximately 3.0Mbps so that is nearly 3.0Gbps. Even when you divide that by the three RAID subsystems we have, that's still 1.0Gbps per system. Since we record 7/24, there is no downtime during which we could perform a backup so it would have to be continuous. That means each storage system would have to write and read 1.0Gbps simultaneously.
Obviously, the better path would be to simultaneously write to two separate systems but that would basically double the cost of already expensive storage. Our solution was to build in as much redundancy as was economically feasible and practical: RAID6 groups of no more than 9+2 disks, redundant controllers and transport and automatic failover systems. Not quite bullet proof but as close as we could get it.
Ok, ok. I'm not a casino so please don't put any money in my slot and pull my arm...
Anyway... To answer the question: over the years, camera counts have increased, as well as bit rates. Some may be surprised to learn that our old system was set to record at ~2 to 2.5Mbps whereas our new system records analog cameras at 2.5 to 3Mbps. h.264 is not much more efficient than MPEG2 and when we switched to a virtual matrix, we chose to keep bit rates high for both "live" and recording to get the best possible image quality.
We keep evidence clips indefinitely - some from as far back as the 1990's. We also save many clips for other departments to review so that the streams don't get overwritten. Most of those eventually get deleted. We also allow certain departments to do their own reviews but unlike some casinos, we make them clips, which they can review in a separate room. Most of them also eventually get deleted.
Many casinos provide workstations with the VMS loaded for outside reviewers and a Surveillance Agent must control playback. We find our way more efficient.
So, yes - we do retain a large amount of data, most of it relatively briefly, but it still is probably orders of magnitude less than 1%.
IPVMU Certified | 04/05/14 09:26pm
Just to make it sure: We are discussing two general different things in the same topic, be careful! RAID is not Backup. Raid is redundancy mechanism, as mentioned a couple of times. A Backup is a "snapshot" of the whole disk or parts of it. A simple example should make clear why it's important to understand the difference. If you just stay with RAID, a disk failure should not affect your recordings. BUT: If a guy with enough rights just deletes Video recordings from yesterday, by mistake or not, those recordings are gone. RAID can't help you here. As you just have redundancy, the recordings will be deleted on ALL your RAID disks at the same time - bang - gone! - That's why a BACKUP could have helped...
Just my thoughts.
A lot of times I've spec'd storage system not using RAID at all. Each disk is alone and not part of a RAID. If there's no need for the redundancy and cost is a factor, and the customer is ok with it, why not? Consider for example you have a 16 bay unit with 3TB dirves. You want super redundancy, you might do RAID6 with 1 global spare. That's 27TB of storage. If you don't use RAID, then that's 48TB of storage.
"What about safe guarding the video?" Well, if something happens to the RAID, you loose all your video. If you loose one drive in your non-RAIDed enclosure, you've only lost 3TB, or 7% of your video. If you loose 3 drives (like the 2 in the RAID 6 and global spare in the example above), you still have 27TB, or 56%of your video. And unless you have need to meet some sort of official requirement or you got big bucks , like was mentioned before, in most cases what's the chance you'll need to go back to that one portion of video that was lost?
That's correct. In fact, the larger the hard disks, the less drives should be in any RAID group. I agree there is a point of diminishing returns, where RAID groups become so small that more disks are dedicated to parity than to actual data storage. At that point, traditional RAID will have become way too inefficient. Although I haven't had much time to thoroughly research alternatives, I understand that there are a few out there, including Drobo's BeyondRAID, Lime Technology's UnRAID, Level 1 storage redundancy and various forms of storage clustering.
I have been approached by a few companies that offer non-traditional storage recently but had other projects in work so I've begged off. I intend to dig deeper as time permits.
Something to look into would be the Veracity Coldstore, does not work with all VMS but a neat solution. http://www.veracityglobal.com/products/storage-for-video-surveillance/coldstore.aspx