If I can give some tips here, having researched this area extensively 3 years back:
- video storage requires loads of storage
- you need to avoid data loss as much as is possible, hence use ZFS
- you need ability to expand
- you still need to backup all this data, hence need a cheap backup box (repurposed old machine perhaps)
- you don't need amazing transfer speeds for streaming
- go for a fairly low-power CPU solution as NAS speeds are limited by the ethernet connection, typically 50MBytes/sec
- disk speeds don't need to be so fast, so 5400 RPM 3.5" drives are fine for video NAS
- to provide against loss, look for double-parity - i.e. 2 drives can die before data loss is experienced (ZFS RAID-Z2, similar to RAID 6)
- use ECC RAM as it helps guard against junk being stored on the drives
Anyway, take a look at the following results of my research, even if it's a couple of years old, it's still relevant:
AMD Athlon II X2 ‘e’ models: AMD have released interesting low power versions of their dual-core 64 bit processors, for example the AMD Athlon II X2 235e . 45W TDP with CPU frequency scaling to use lower power when the NAS is idle. As with most AMD processors, these provide ECC memory support within the memory controller within the processor package.
Go for a well-supported, reliable socket AM3 motherboard. I have had a lot of success with Asus motherboards using AM2 socket motherboards. Make sure the chipset is well supported (NIC / SATA etc), and has six SATA ports on the motherboard (see drive tips below for why six is a good number).
As video storage requires lots of capacity, you'll want to use large capacity drives. The 2TB drive is currently the largest capacity drive easily available, but high reliability has become difficult for drive manufacturers to achieve. The most reliable consumer-priced drives that I have found this year are Samsung HD203WI drives (4-platter, 2TB, 5400 RPM), which I personally use without any problems/errors detected, and there is a newer model, Samsung HD204UI (3-platter, 2TB, 5400 RPM) which is worth checking out.
Also, to use double-parity (ZFS RAID-Z2 / RAID 6), the capacity of two drives will be used to provide storage for parity data, so to enable a good data-to-parity ratio, a six-drive setup will allow you the capacity of 4 drives for data and 2 drives for parity data, so 2/3 of the capacity is used for data, and 1/3 for parity data. E.g. using six 2TB drives, you'll get approximately 8TB for data and 4TB for parity data.
Finally, let me re-emphasize the importance of using a robust file system like ZFS, which has superb RAID features. Use OpenSolaris build 134, as it is the last release before Oracle clobbered OpenSolaris. OpenSolaris forks called OpenIndiana/Illumos have appeared to replace the open-source OpenSolaris and these will take over from OpenSolaris. Also FreeBSD has a port of ZFS, but the OpenSolaris version is preferable as it has rollback capability so you can recover the OS from a failed upgrade, and this feature is called Boot Environments, or BE as an abbreviation.
Some people also recommend Nexenta, but be aware that this is a commercial company, but there is a free version that allows up to 12TB. Personally, I like to avoid "free up to a point" products, so I chose OpenSolaris. As OpenSolaris is now dead, look for the successors: OpenIndiana/Illumos. Or just install OpenSolaris build 134 now, and migrate to OpenIndiana later once they get properly under way.
Hope it helps, and feel free to ask if you have questions after reading the URL I listed above.