Solid State Drives Useful For Nvrs?
Milestone's Husky NVRs are using SSDs for the OS and VMS drive - which led to a discussion in our office about when do you expect to see SSDs used for video storage? Aside from the current issues of limited size and high cost, what about their durability in a VMS environment? I've read SSDs have a finite number of times they can be written to - is this something that can be overcome? I'm interested in everyone's thoughts.
In mobile markets (school busses, public transit) they are becoming increasingly popular due to being less susceptible to vibration.
One side note: SSDs for OD / VMS application have been fairly common in professional recorder appliances for a while.
As for video storage, that's a good question. I don't have any experiences with that.
"Today's commodity 2D MLC flash has raw wear-out in the 2,000 to 3,000 write cycle range.
Pioneers of 3D flash say their SSD endurance is better. But how much of that is due to more expensive substrate materials and how much is done by the controller isn't clear yet. So for the purposes of this article everything below is about 2D (planar) nand flash.
The future direction of endurance is downwards (towards worse). Also - SSD designers have reported that when they have measured endurance in this classic way - the specs in recent flash generations are tighter than they used to be - with less headroom.
Long article, but reading it makes me believe SSD RAID would be viable for video recording. After all, the author states "Why, for example, does the data recorder example stress a flash SSD more than say continuously writing to the same sector?
The answer is that the data recorder - by writing to successively sectors - makes the best use of the inbuilt block erase/write circuits and the external (to the flash memory - but still internal to the SSD) buffer / cache. In fact it's the only way you can get anywhere close to the headline spec data write throughput and write IOPS.
This is because you are statistically more likely to find that writing to different address blocks finds blocks that are ready to write."
Two of the main reasons for using an SSD for storage are speed of a single drive, and shock tolerance. I think it is still fair to say that neither of these factors are important for most VMS storage purposes.
I previously worked at Blackmagic Design for a decade where SSDs were used for storage in their video/film cameras and disk recorders. SSDs were ideal because they could capture RAW and uncompressed HD1080p video (and higher resolutions) on a single SSD because the media was so fast. This avoided the need to use video compression and so no quality was lost. As SSDs are much more tolerant to shock and vibration, they were ideal for field use in cameras and portable disk recorders where hard drive failures could have been expected.
Most VMS storage installations do not need to be portable and nor do they benefit from the compact, very fast media speeds provided by SSDs. While the cost of SSDs has dropped significantly, they are still much more expensive than equivalent-sized hard drives. Furthermore the biggest hard drives are currently about 4 times the size of the biggest SSDs. A disk array of conventional hard disks can provide plenty of speed, high capacity and can also offer redundancy in case of hard drive failures.
At such a time as SSDs get close in per gigabyte pricing to hard drives, and get closer to the storage capacity offered by hard drives, that will be the time for VMS storage to use SSDs. Until then, I would recommend using hard drives unless portability or shock tolerance factors are of concern.
Finally, I am cautious about the use of edge storage in IP cameras. Flash memory cards are not designed to tolerate the amount of reading and writing which occurs during typical computer use. I think it is OK to use edge storage in addition to an NVR but I would be wary of relying upon edge storage as the only form of storage.
In the VMS systems we manufacture, the SSDs are relegated to OS and Rugged-Mobile usage as has been mentioned here. We do have 1TB SSD we use in some builds, but that one is very costly right now.
We typically do NOT use them for the normal system video storage due to the capacity, cost and wearout mechanisms.
With that said, the SSD technology is getting better at handling the write endurance issue. Some Vendors/Controllers are better than others.
Here is a reference to a test specifically created to test write endurance.
I have my Windows Worktation NVR's built with a 64gb ssd for the OS and then I use the proven surveillance grade HD's for recording. Cost stays down and reliability and speed is stiil good. Keeping the OS on seprate drive makes it easier to rebuild if a drive does fail.
S2 has done a lot of work on solid state storage because we've featured a solid state offering in our access control line for 10 years. In the access control application, writing tends to be random and occasional, as in record updates, or sequential and frequent, as in history record writing. These application characteristics are great for SSD, and rewrite life has minimal impact on the analysis.
Video is another story. Three things keeps us from using SSD in video applications: rewrite life; need to erase blocks before writing even partial blocks; and of course, cost. A lot has been said about rewrite life and cost. The fact that blocks need to be erased before being written - the disk does this in its microcode for you automatically - means that the time required to actually write sectors can be variable.
That said, I'm looking forward to when SSD technology works in the video application. Then all we'll have to worry about is heat generated by the processor!
Another thing to keep in mind about these SSD's is not just how often they fail, but often how they fail... There is something comforting in the design of the mechanincal platter in 'legacy' hard drives. Depending on the circumstances, not even considering things like S.M.A.R.T., you might have a lot of warning before failure, noisy seek errors, blue screens, Concorde takeoff level sounds etc, before a crash.
Even more comforting was the fact that you really felt your data was "written" as in etched somewhere and even if the seek arm decides to dip and gouge the substrate at 100MPH, we knew the rest of the data is still there somehow, even if we have to play two grand for someone in a clean room to get it!
In my experience SSD's (5 total losses and counting), often seem fine one second, at then the whole volume is instantly gone. Or maybe you have experienced the shrdsk version of chkdsk where to your horror chkdsk decides that every file on your drive is really an orphaned cluster and creates a mountain of rubble in your recover directory. Tech support might even have the nerve to tell you that, "you actually you haven't lost any file data.". This causes one to ruminate wistfully on the value of meta-data at length.
I had a case where the whole volume will come in and go out every three or four seconds all day. Most disconcerting is the fact that you just don't feel like if you really needed it the data is there somewhere... At least I don't...
we have always built our own NVR's and we always use a solid state hard drive for the operating system. We find it to be a very stable platform for the OS. We use enterprise class HDD for recording, and are trying the new purple HDD from western digital for our new NVR's as they are being touted as being built specifically for CCTV recording
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