Registered versus Unbufffered RAM

[vodkaman]

Hi Everyone,

I've done a TON of reading and have not found a clear answer on this. All sites say that when using large amounts of RAM you should use registered RAM however it doesn't say if this large amount refers to the number of size of a SINGLE RAM chip or the entire lump sum of RAM on the server.

To elaborate, I saw a site that said anything equal to or greater 4GB should use registered ram - does this mean 4GB or over on a SINGLE chip?

After researching it seems as though the problem registered ram solves relates to a single RAM chip being very high density... Meaning the it relates to a single chip. Some sites also state that with smaller RAM registered can even hurt speed.

The reason I ask is because we're putting 24GB into a server however it will be made up of 12 2GB chips. The cost difference between registered and unbuffered is a good amount and with budgets the way they are I'd rather not spend it if it's not needed and could even be detrimental.

I know that the generic answer is registered is better but it seems it's not that clear.

Does anyone here know the super fine details of this? Thanks for the help

 

[tf1]

Standard unregistered RAM is faster than registered RAM. Registered RAM may be up to 5-15% slower than standard RAM because it runs a clock-cycle behind. (It depends on RAM type, single or dual channel and bus speed.)

That said, registered RAM on server motherboards does have advantages. The system is able to detect bad RAM, disable it and provide an Admin message stating the problem. More sophisticated motherboards let you install spare RAM so that detected errors disable the bad module(s) and switch over to the standby modules.

In my many years of experience with servers, I cannot recall ever having a RAM module fail, but it does happen. So it is down to risk assessment. How much does temporary downtime of a server cost your business? If you have many users unable to work during server downtime or if you have crucial orders passing through your server, then the investment in Registered ECC RAM is worth the extra. If half an hours outage isn't critical, then go for standard RAM.


Regards: Terry

 

[vodkaman]

Hi Terry,

Thanks for the feedback - much appreciated.

I understand everything you're saying but I don't see a conclusive answer in your post to my specific question. I already understand what registered ram is.

Common knowledge is that registered ram only makes a difference when there is 4GB of RAM or more - my question is, is that 4GB PER RAM CHIP or 4GB total RAM in the ENTIRE system?

From the significant reading I've done on the subject I've never found a conclusive answer, only unclear insinuation.

 

[tf1]

From experience (back in the days when RAM was worth more than gold and a server with 8GB RAM was kept in a locked cage) it is by quantity. We used 4 x 1GB or 8 x 1GB registered ECC modules back then, which makes me assume it is the total installed quantity irrespective of module size.

I also found this

http://images10.newegg.com/UploadFi...Do_I_Need_ECC_and_Registered_Memory-v1.1e.doc

It doesn't look exactly a scientific document but it does say 'more than 4GB per system' and I have no reason to doubt it.

Regards: Terry

 

[vodkaman]

Thanks for the feedback Terry - registered it is.

 

[cdogg]

The whole point of using buffered (registered) over unbuffered is reduce the strain on the memory interface as the amount of memory increases. Here's an article that goes into more detail:

http://www.servethehome.com/unbuffered-registered-ecc-memory-difference-ecc-udimms-rdimms/

4GB is likely outdated. It probably dates back to the time when the memory controller was still integrated in the Northbridge. Now that Intel and AMD have moved onto faster interfaces with the memory controller integrated directly onto the CPU die, I would bet that "line in the sand" has moved to 16GB or even higher.


Carl

"Nearly all men can stand adversity, but if you want to test
a man's character, give him power." - Abraham Lincoln
[tab][navy]For this site's posting policies, click [/navy]here.

 

[hairlessupportmonkey]

without question, you should be using 24GB of the best quality RAM you can afford in a server. You are looking for reliability slightly over speed. Buffered ECC RAM would be my choice especially when you start using large RAM sizes... more memory, more potential errors. RAM errors can cause all sorts of issues, least of all blue screens!

ACSS - SME
General Geek

 

[cdogg]

monkey,
You are promoting the use of ECC over non-ECC for "reliability". ECC is a must in any server. I don't believe the OP was ever doubting that.

Buffered vs. unbuffered is a different kind of comparison. It is less about reliability than it is about speed. You can use unbuffered ECC and be just as reliable as you would with buffered ECC. The difference is that unbuffered will run much faster in low virtualization or low consolidation environments where the amount of memory bandwidth required is relatively low. Buffered, on the other hand, will run faster in situations that do require a lot of bandwidth and large amounts of memory, simply because the strain on the memory controller would be too great with unbuffered.

However, it's important to realize that many high-end systems that support a large amount of memory require buffered ECC. The reason is that buffered memory reduces the complexity of the motherboard's design which is the reason the board can support a large amount of memory to begin with.

Carl

"Nearly all men can stand adversity, but if you want to test
a man's character, give him power." - Abraham Lincoln
[tab][navy]For this site's posting policies, click [/navy]here.