I've inherited a barebones old Compaq tower from a friend for free. The mobo is Asus, socket 775 and currently contains a Pentium D 2.8Ghz CPU.

I think it's this one.

It's got an old GeForce GFX card and no HDD. I will be ripping out the GFX and selling it off cheap.

The Pentium D in question is 95W TDP and I'd like to remove it and put in something a lot more power efficient, then add a cheap PCI-E RAID controller and a couple of 2.5" HDD to use with something like FreeNAS software.

The box looks crappy, but I don't mind as I plan to stick it under a table in a spare room where it won't be seen. Plus I'm getting it for nothing.

I'd also take out the PSU and run it on a PicoPSU or something equally low wattage.

My main aim is to use as little power as possible and not spend too much.

Will I be able to achieve low power consumption with a different LGA775 CPU?

Is the mobo and chipset so outdated that I would be better off binning the hardware and getting a cheap mini-ATX/CPU combo board?

I'd like something that consumes less than 30W when idling/streaming video over LAN, so that it doesn't crank up my electricity bill. Is this possible?

I'm all for reusing old hardware, but for a simple NAS I think you're better of with something like Bay-trail. I would at least do some calculations to estimate how much you would save by reusing the socket 775 system. And also perhaps how much electricity would cost over time.

Also PCI-E RAID controller and 2.5" HDDs isn't exactly low end. Strange to couple that with an old system so save a few bucks.

Hmm, Baytrail certainly looks a good idea for a long term energy saver.

Dual-channel RAM too, which is a bonus.

And how about 2 x SATA in RAID-1 using software RAID? The extra money spent on buying a new mobo would be saved by not needing to buy a RAID card.

I'm liking this idea and could mount it in the crappy tower case until I get around to funding a mini-ITX one.

Is two port software RAID-1 under FreeNAS good enough for streaming HD movies?

If the above is true I think I'm sold on this idea.

Streaming HD movies is not very demanding. Almost any setup could handle that.

What are your priorities with this NAS? Silent? Cheap? Reliable? Low power? I mean, you could use the socket 775 as it is, maybe just put a larger HDD in there. And a backup drive on the side. Cheap and pretty reliable. RAID is only useful to secure uptime, is that important?

I think the network interface would be the limiting factor (a wired Gigabit could be considered the minimum requirement for uncompressed HD), not the CPU or the software RAID. Anyway, IIRC currently BayTrail GPU may have issues with some 'nixes, like FreeBSD.

Any RAID card that is cheaper or even close to a new Baytrail MB (~$100) is not worth it. Software RAID will be better. RAID 0 or 1 has almost no CPU impact and RAID 5 or 6 is still very low on any even remotely modern CPU.

As always, RAID is not a backup. If you can only afford 2 drives then use one as a backup, don't use RAID 1.

The streaming wouldn't be uncompressed though, would it? If I'm streaming a mp4 or mkv file all of the decoding would be done on the client device, such as my main PC or Raspberry Pi. The file size down the network would still be its normal, compressed size. Same as if I was accessing a document file. My home plug network currently works fine with an 8gb mkv streamed to the Raspberry Pi.

I think I'm sold on the idea of the cheapest Bay Trail because of low power consumption, maybe powered by a pico psu. Still unsure about which software RAID configuration, though.

Double post due to using my phone browser.

In spite of baytrail, you will have a hard time beating a 2-bay QNAP or Synologie prebuild NAS in power consumption.

If you are happy with the supplied functions, a prebuild NAS should rule the power charts.