3 sticks of RAM in a dual channel system?

[Suspicious-Teach8788]

Ok, so here's the story. I'm building a NAS. I have a i7 right now with 3x2gb RAM. It's plenty, but RAM prices are DIRT cheap right now. I could get 2x2gb for my new NAS, but 2x4gb is pretty dirty cheap too (esp the slickdeal today). But here I'm thinking why would I even buy that much RAM for a NAS right? Even if I use ZFS and pound it with plenty of access, 4gb should be plenty. The fact that I could put more in my NAS than my main workstation bothers me

Now, then an idea popped up. Why not just buy 3x4gb, stick it in my i7 rig, pull the 6gb and slap it in my new NAS. Would I be better just using 2x2gb and leaving 1 stick sitting out or just use all 3? I'd be losing dual channel bandwidth though?

 

[IntelUser2000]

You'll be "dual-channel", but with a caveat. Read on to see if its worth it.

The Intel systems since Core 2(or a generation before that) supports asynchronous dual channel operation called Flex Memory. It allows you to get dual channel support using different capacities per channel.

Like in your case, 8GB in one, and 4GB in other. The way Flex Memory works is the amount of memory you have in your lower capacity channel would "dual-channel" the same amount in the greater capacity channel. What's left over will work just as it was on a single channel setup.

Asynchronous Dual Channel

Channel 0
DIMM 0: 4GB
DIMM 1: 4GB

Channel 1
DIMM 2: 4GB

4GB= Dual channel operation, 4GB=Single channel operation

The problem is how it works in reality. Bandwidth measurements will put it smack dab between 2-channel and 1-channel setup. It's like a 1.5-channel. But the process of allowing asynchronous operation will lower the performance further. It's probably closer to 1-channel than 2-channel in applications not particularly sensitive to memory bandwidth.

Just accept the fact that your NAS system will have more memory than your i7 high end system and get the 2x 4GB sticks.