Two parts here… First your answer..
There is no hard and fast rule that will always predict the "best" RAID. YMWV (Your Mileage Will Vary)... RAID5/6 with parity is a controller specific/vendor specific tunable system. Nearly always, "it depends" on both how you have it set up and how you use it.
For example, a full stripe write of say 1MB chunks (8D+1P RAID5 -> 128KB x 8 = 1MB ) allows the controller to write 128KB to each disk (assuming this is the segment size or a multiple of it). This means that the parity ASIC in the controller does not need to read any disk blocks, only calculate a new parity value on the fly and just write away. That means you have 8X the sequential throughput of a single disk drive for both large sequential reads and large block writes. A RAID 10 array with 10 disks has only 5 unique storage locations and so typically has a peak of <5X for sequential writes as both disk have to keep up. Reads can be either 5X or 10X or somewhere in between depending.
Some RAID vendors even license bottlenecks... The storage system is capable of 3X performance, but they sell it for a lower price with a governor installed providing 1X but still good numbers. Installing a new license key, uncorks it and the system performs MUCH better...
Now the philosophy…
We could go over a bunch of examples, but my purpose is more to illustrate how to fish than just put fish in your basket if possible. Kind of like memorizing a multiplication table, instead of learning how to multiply... The table is very fast to recall, but severely limits your options. It also assumes you memorized every possible scenario. I can’t predict the future that well… The skill of multiplication is much more valuable.
By learning to watch some very basic Windows Perfmon counters (Linux has them as well), you can nearly always make a good choice about the effective use of money and technology to solve or avoid performance problems.
Remember that Windows7-x64 really is Server 2008R2 under the covers. Download one of the Microsoft Server tuning guides. http://msdn.microsoft.com/en-us/library/windows/hardware/gg463392.aspx They are surprisingly readable. You are really designing a server with a VMS/DVR…. Just on a smaller budget…
Spend an hour or two with a few cameras recording to a disk and play with the camera encoding parameters. Crank up the frame rate and the resolution and turn down the compression. Switch to MJPEG even and run it at night during the snow with flood lamps on or in the dark with the gain WAY up. Have the cameras watch an action movie, a TV channel of noise/static/snow, or point them at a spinning fan which fills the frame…
Just the opposite of what you would normally do. :-)
Use Perfmon to watch the NIC throughput, the disk queue, the disk latency, disk transaction rate, the CPU loads, Memory, etc.. Learn how what you change affects the overall system workload. Try a single disk instead of an array. Try turning on and off the RAID write cache to see what happens… Maybe download one of the many free benchmark utilities and see how your tuning affects sequential versus random I/O numbers.
Modern Nearline SAS or SATA RAID5 volumes are HUGE. What do you do with a 16TB or 24TB volume? How long does it take to rebuild from a failed disk? Days? What if a bad block is found during the 20TB 3-day rebuild (it happens fairly often)?
In this sort of scenario, maybe RAID6 is better? Test it and see… While a RAID volume is rebuilding, how are the Perfmon numbers compared to before? Can you even keep the cameras running? Is a 4-drive RAID6 better than a 4-drive RAID10? How many IOPS does each camera add to the disk system? How many can your design handle with the disk transaction times staying below 5-10msec?
Just tinker with it for even a ½ a day… This sort of time and information will pay you back immensely with your better systems design and overall understanding.
Very few real performance problems exist today that cannot be solved or avoided quite readily. Nearly always, the problem lies in the design choices. Sometimes there is a cost to resolve it. (a good design is not free) Learn to identify where the root cause of the problem and this will greatly reduce the waste of your time and/or money regardless of the source...
Listen and learn from the vendors, but they are selling something so pay attention, but do not blindly follow them. Put more trust in independent studies/reviews than any single vendor. (that is why you are here, right?) A solution has to work for YOU and your customers, or it doesn’t matter how cool/fab/fast/etc… it is to someone else… Ultimately, we are all paid to solve a problem for someone else. They barter their time to earn money, for our time to solve their problem with a solution.
No matter how much someone knows about this stuff, they can’t tell you in advance whether you need more CPU cores, or fewer faster ones, or more RAM or more disks, or RAID Cache or NICs, or switches, etc.. without measuring what you have and how you use it first. But, with a little time spent learning this stuff, you will be able to do so while you build/install/support the systems you put together. You will learn that the A+B+C combination needs XYZ solution and more importantly, you will know why and how it should change for the next one.
(BTW, this works just as well for playback issues as well on the workstation side. Same song, different verse...)
Sorry for the long post, but you would be surprised how often this exact type of problem comes up...