RAM: Fully Buffered vs Registered (& unbuffered/unregistered)

[SHA256]

14 years in computer support, so I know some general terminology, but I'm no sysadmin (except for two hellish years running an ubuntu dhcp/dns/file server, but I was making it up as I went along. I didn't build that computer either; I think it was desktop-class though).

My question is this - there's not much that I could find googling around either. (edit: I was able to find this article, through freenas forums, at least explaining the difference between registered and buffered - but does not mention "fully buffered") What is the difference between FB RAM and Registered? I know there's a chip controlling ...something... on the former. Newegg shows those four categories under server memory.

Obviously Registered is the most common (239 hits on newegg at this moment, vs 25 for FB). But there's also 87 hits for "unbuffered." All this is still listed as ECC RAM (<-- newegg link) though, so I want to ask the experienced folks here:

What's the best for FreeNAS of those 4 options? Am I right in assuming that FB is "best" in general, but can FreeNAS and ZFS take advantage of its powers over Registered? And what about unbuffered - should it even be considered as an option? If people have the cash to shell out for it, is FB always the best option or is it not worth the price and I should stick with the much-more-common "registered" ECC?

And is "unregistered ECC" memory (1 hit on Newegg) even ECC at all?

Thanks!

 

[danb35]

To the best of my knowledge, all are ECC, and which one is appropriate depends on your CPU/motherboard combination. As I understand it, only one of those options will work with any given configuration, so that's the one to use.

 

[Ericloewe]

ECC has absolutely nothing to do with memory being registered or not (in practice, all registered memory is ECC, due to its target market).

Desktop stuff and related products (Intel consumer CPUs and Xeon E3s) only support unbuffered memory.
Some higher-end stuff may support registered RAM - this requires reading what the manufacturer has to say.

Registered memory uses registers (think of them as buffers) to reduce electrical loading on the memory controller, allowing more RAM chips to be used, which allows for higher-capacity DIMMs.
ECC uses 1/8 more memory to store an error-correction code (that also detects errors larger than one bit, but can't correct them).

Check your motherboard's manufacturer's webpage for the Hardware Compatibility List and get memory that's listed there. Check the motherboard's specifications and you'll quickly find out whether you need Unbuffered or Registered.
I'll venture a guess that it's unbuffered.

 

[SHA256]

ECC has absolutely nothing to do with memory being registered or not (in practice, all registered memory is ECC, due to its target market).


Check your motherboard's manufacturer's webpage for the Hardware Compatibility List and get memory that's listed there. Check the motherboard's specifications and you'll quickly find out whether you need Unbuffered or Registered.
I'll venture a guess that it's unbuffered.

Thank you. Let's say I had the cash to burn to get (what looks to me) one of the most-commented on boards on these forums, the X10SL7 supermicro. From the specs on it, it says it supports "up to 32 GB DDR3 ECC Un-Buffered memory (UDIMM)." Does this mean that "fully buffered" RAM won't work on it? And the word "registered" is never mentioned on that page - I just know that it's rated for "un-buffered" but it doesn't say anything about registered.

I guess I'm still hoping that someone can answer my question - is Fully Buffered better, no difference, or worse than unbuffered for FreeNAS's purposes?

 

[danb35]

No difference. Use what's compatible with the motherboard and CPU you choose and be happy.

 

[toadman]

Buffered memory is used in systems that require a large number of DIMMs. So I agree with danb35, makes no difference for FreeNAS all else being equal. If you need more than 2 dimm slots per memory channel, the board will probably require buffered dimms. It's rare (these days) that a board would support both buffered (registered) and unbuffered.

So get a board that supports the amount of RAM you need, then get memory that matches what the board requires.

(BTW, "fully buffered" memory is different entirely than "buffered"/"registered". FB-DIMMs are a technology Intel had in it's servers.)

 

[SHA256]

No difference. Use what's compatible with the motherboard and CPU you choose and be happy.

Thanks! Good to know. It will help keep prices down to go with "merely" registered memory instead of fully buffered stuff. So, as for that expensive X10 board up above...it doesn't say registered, it only says unbuffered. Does this mean that registered memory will not work with it?

edit: just saw toadman's post. Does this mean that on this list of 11 ecc, 32GB ram sets, I should only pick the 2 that are unbuffered, and leave the 9 registered ones alone? (once again "perfect world" kind of build...I might be coming into some money soon and I'd like to future proof this bad boy as much as I can)

 

[danb35]

Yes.

 

[Ericloewe]

Thanks! Good to know. It will help keep prices down to go with "merely" registered memory instead of fully buffered stuff. So, as for that expensive X10 board up above...it doesn't say registered, it only says unbuffered. Does this mean that registered memory will not work with it?

edit: just saw toadman's post. Does this mean that on this list of 11 ecc, 32GB ram sets, I should only pick the 2 that are unbuffered, and leave the 9 registered ones alone? (once again "perfect world" kind of build...I might be coming into some money soon and I'd like to future proof this bad boy as much as I can)

Do not buy Registered if you're using a supermicro X10 motherboard (or any other motherboard for LGA1150).

You need Unbuffered.

Unbuffered != Registered != Fullly Buffered

 

[SHA256]

Thanks for the help and clarification, everyone! Fully buffered (and its value) was the main question here, but you also just cleared up everything else, too!

 

[toadman]

For historical purposes, the production of fully-buffered DIMMs occurred because Intel got stuck on it's roadmap and couldn't make an architectural transition when needed. FB-DIMMs and the AMB that went with the chipset were a patch.

In other words, the "value" of the technology was to Intel, not to the end consumer.