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As a rough indication of the speed you will be achieving on the various arrays you mentioned:
1. 7 x raid5 plus 1 hot-spare: around 600 MB/s
2. 8 x raid50: around 500 MB/s
3. 4 x raid0: around 400 MB/s
That is only about speed, but safety is another matter. With 12 disks available, I would consider an alternative setup like this:
8 x raid5 plus 1 hot spare (around 650 MB/s) and 3 x raid0 (300 MB/s) for cache, previews and pagefile. Your exports should not go to the raid0 but to the raid5. This approach will give you even better speed on the raid5, dual disk failure protection and sufficient raid0 speed even with 4:2:2 material.
SATA2 or SATA3 will not make much difference, the raid controller and the amount of cache memory on the controller will have a much bigger impact.
Just my 0.02
The reason you mentioned a 8+1 RAID5, instead of a 7+1, other then the added transfer rate speed, and other then the fact that it takes a 16 port card instead of an 8 port, is it more efficient and measurable to have data stripped in byte sized numbers (or divisable byte sized numbers), such as 16, 8, 4, 2)?
I dealt with a video systems integrator here in Montreal, and they don't suggest RAID3, but rather RAID5. He is a reseller of Areca, and Atto (his preference is mostly Atto). I know you are a big advocate of RAID3. I also knot that RAID 5 is an ideal solution for multiple access systems (such as file servers). I also know that RAID 3 is perfect in a single user, stand alone configurations for large files. Other then the fact that RAID 5 on modern controller cards are relatively efficient, and RAID3 is considered "old", what I don't know, and would like to, is, what's the real-world data transfer advantages of one over the other in an editing environment. Areca seems to be the only one to maintain hardware RAID3, so obviously, they understand something that other manufacturers don't?
If my computer is hooked up to a UPS, is a BBM for the RAID card a necessity? Or would it only serve as a second level redundancy?
The major difference between raid5 on the one hand and raid3 or raid4 on the other hand is distributed versus dedicated parity.
All three raid formats are quite good but in some cases one may be preferred over the other.
What is the difference between dedicated or distributed parity?
In the case of distributed parity, a rebuild of the array requires W actions on all drives.
In the case of dedicated parity, a rebuild will require W actions on all drives minus one.
For this simple reason the rebuild will be more efficient with dedicated parity than with distributed parity. Raid3/4 are more efficient with rebuilds than raid5.
ATTO is a rather unknown brand amongst consumers, but they are the only one to offer raid4.
Areca is relatively well known, even amongst consumers and are the only one to offer raid3.
You mentioned 12 disks, so from that perspective I made my suggestion for an alternative configuration.