4GB or 8GB RAM - to DualChannel or not?

Does unRAID have any benefit of DualChannel RAM? Or does it care about the amount of RAM?

I have just ordered the Silverstone DS380 chassis and is about to finally build my server but have the option of using one or two sticks of RAM.

Sorry to not have any unRaid specific info, but I always encourage getting more RAM than you think you need.  If you're going to be running a vanilla unRaid server and no add-ons then 4 GB is probably way more than you need.  But RAM is pretty cheap compared to the system costs, and you may get a slight performance increase with dual channel.  My rule of thumb for any new build is 2x4GB minimum, simply because if I repurpose the MB for something else it has enough RAM to be useful.

Does unRAID have any benefit of DualChannel RAM?

A technicality, but there is no such thing as "Dual Channel RAM".    Dual channel is an operating mode of the memory controller which it can take advantage of when you have 2 modules with identical specifications installed (actually modern controllers can operate in a less efficient dual channel mode even if the modules are different).    Whether or not your system can operate in dual channel mode depends on the specific motherboard and chipset you're using; but most modern systems do support dual channel operation.

... does it care about the amount of RAM?

Not sure it "cares"      ... but yes, it will use the additional memory; and in particular many of the plug-ins/add-ons will run better if they have more memory available.

I have just ordered the Silverstone DS380 chassis and is about to finally build my server but have the option of using one or two sticks of RAM.

I'd always use 2 modules to ensure the system was operating in synchronous dual channel mode.

What motherboard are you using?

 

A technicality, but there is no such thing as "Dual Channel RAM".    Dual channel is an operating mode of the memory controller which it can take advantage of when you have 2 modules with identical specifications installed (actually modern controllers can operate in a less efficient dual channel mode even if the modules are different).    Whether or not your system can operate in dual channel mode depends on the specific motherboard and chipset you're using; but most modern systems do support dual channel operation.

Sorry, thats what I meant - RAM set up in Dual Channel mode running off my CPU's build in memory controller that supports it.

The question was more if unRAID would have any benefit of that or I could just use a single stick of RAM without any performance penalties?

Not sure it "cares"      ... but yes, it will use the additional memory; and in particular many of the plug-ins/add-ons will run better if they have more memory available.

Cool, but that leads back to the first question if it matters that I have 8GB running in Dual Channel or I have them on a single stick?

I'd always use 2 modules to ensure the system was operating in synchronous dual channel mode.

What motherboard are you using?

Ok, but then again, does unRAID work better in synchronous dual channel mode? And if you know, why does it do so?

I currently have a Gigabyte GA-B75N I would like to use with a intel i3-3225 and two Corsair Vengeance LP 1600MHz CL8 4GB sticks for a total of 8GB. But very soon I will buy a AMD 5350 and a Asrock AM1H-ITX that could also be used, the AMD only supports single channel RAM (in my case 8GB Geil NT 1600MHz CL11) and I would prefer to use that build as my new HTPC because of the stronger iGPU.

The OS isn't involved at all in whether or not a system runs in dual channel mode ... so the answer r.e. UnRAID working better with dual channel is simple:  if the motherboard supports dual channel, then if you install 2 modules the memory accesses will benefit from the improved bandwidth -- whether UnRAID or any other OS.    If the board doesn't support dual channel mode, then it clearly doesn't matter.  In the latter case, not only does it not make any difference in performance, but it's electrically better to use a single module, as the loading on the bus will be lower (thus cleaner signaling waveforms).

The OS isn't involved at all in whether or not a system runs in dual channel mode ... so the answer r.e. UnRAID working better with dual channel is simple:  if the motherboard supports dual channel, then if you install 2 modules the memory accesses will benefit from the improved bandwidth -- whether UnRAID or any other OS.    If the board doesn't support dual channel mode, then it clearly doesn't matter.  In the latter case, not only does it not make any difference in performance, but it's electrically better to use a single module, as the loading on the bus will be lower (thus cleaner signaling waveforms).

Actually I had never thought about it like that, but it makes perfect sense. Anyway, I already have the dual channel set so I will just use it as it is for the server.

Thanks for all the help

Sorry to hijack but it's a quick question and it's relevant to the topic.

I have a HP Workstation Z230 SFF with 4 dimm sockets available.

Now I use 2x2Gb ECC ram probably in dual channel as it came from the manufacturer.

I want to upgrade and I plan to ADD 2x4Gb to get total 12Gb.

Will I lose the dual channel bonus using 2x2 and 2x4 modules?

Is each channel individual?

I asked at the store I plan to buy them from and this is what the told me.

Thanks in advance!

Will I lose the dual channel bonus using 2x2 and 2x4 modules?

No, the system will still operate in dual channel mode.

Will I lose the dual channel bonus using 2x2 and 2x4 modules?

Is each channel individual?

In a 4-slot-2-channel arrangement , the way it works is each channel has 2 slots. If you read the motherboard manual, it would tell you something along the line of add RAM sticks to the slots in this order. That is to ensure you don't end up adding 2 sticks to the 2 slots that share the same channel.

In your case though, it should still be in dual channel mode as garycase mentioned.

thank you both,

this is what I knew

You're welcome.  One more note:  I assume you know this, but since you're using ECC modules be CERTAIN that the modules you buy to add are also ECC modules.    They have to be unbuffered ECC modules, as that system can't use registered modules.

One final thought:  With unbuffered modules, your memory will actually be more reliable if you only install 2 modules (due to bus loading).    You may want to consider simply replacing your 2 current modules with a pair of 8GB modules ... giving you 16GB total memory while only loading the bus with 2 modules.

Note about ECC: I know that, thank you.

About 2nd note:

As I have no experience at all with ECC memory I didn't know that.

As it's difficult to sell 2x2Gb ECC memory, I have to install it to a identical system at work without really any need for this. Just to use them somewhere.

Also, I should spend instead of €62 for 2x4Gb = 12Gb total , €114 for 2x8Gb = 16Gb total. Almost double the money without the need for the extra memory.

Is it going to be unreliable (trying to understand the term "more reliable")? I believe not.

Have you seen a live case or is it the theory?

Isn't it the same with "the more data put into memory the more likely is to have a fault"!?

It's my first Xeon cpu and ECC memory!

Of course I will memtest and I can do it for several days to be extra safe.

No, it's won't be "unreliable" => and since they're ECC modules even if you get an occasional bit error it will be automatically corrected anyway, so since the cost difference is so high, just go with your original plan.

Bus loading isn't because they're ECC modules -- it's because they're unbuffered.  Unbuffered memory modules put one "load" per CHIP on the memory bus -- which typically means 16-18 loads per module (18 for ECC).    This loading results in a deterioration of the signaling waveforms, which reduces the overall reliability of the memory subsystem.  That's why higher-end systems use buffered modules ... with a buffer chip on the module there is one load per MODULE ... so the waveform is very stable.    This is not just theoretical deterioration -- it absolutely happens.    That's why most servers use registered (buffered) modules.    Watch Item #10 here if you want a bit more detail:  http://www.xlrq.com/stacks/corsair/153707/index.html

No, it's won't be "unreliable" => and since they're ECC modules even if you get an occasional bit error it will be automatically corrected anyway, so since the cost difference is so high, just go with your original plan.

 

Bus loading isn't because they're ECC modules -- it's because they're unbuffered.  Unbuffered memory modules put one "load" per CHIP on the memory bus -- which typically means 16-18 loads per module (18 for ECC).    This loading results in a deterioration of the signaling waveforms, which reduces the overall reliability of the memory subsystem.  That's why higher-end systems use buffered modules ... with a buffer chip on the module there is one load per MODULE ... so the waveform is very stable.    This is not just theoretical deterioration -- it absolutely happens.    That's why most servers use registered (buffered) modules.    Watch Item #10 here if you want a bit more detail:  http://www.xlrq.com/stacks/corsair/153707/index.html

Big thanks for this excellent description.

From your post, I would buy the 2x4 and use 4 dimms.

From the slide, especially the note about "most desktop chip sets designed for 32 address load"

So with my 4 dimms unbuffered will have 36 address load when with buffered just 32!!!!

So why do the provide 4 dimm slots!!!

Also, if fault happens because of the address load, the ECC will recover it so there would be only a performance hit. Not reliability problem.

If the above is correct, buffered would be mostly beneficial for high memory usage >>12Gb and with high memory reads/writes.

I don't believe it will affect copying of photos/videos that I mostly care about!

This is my motherboards chipset but I can not find the "design of memory load"

http://ark.intel.com/products/75522/Intel-DH82C226-PCH

... So with my 4 dimms unbuffered will have 36 address load when with buffered just 32!!!!

Actually it's likely even worse.  Look at your memory modules and see how many memory chips they have on them.  Many have 16/18 chips per module => if that's the case 4 modules will preset 72 "loads" to the bus.    But the slightly extra load you get with ECC modules is definitely worth the extra protection they provide.

... So why do the provide 4 dimm slots!!!

Good question.  I'd really like to see buffered RAM support on desktop chipsets; but with a few (rare) exceptions that's simply not the case.    If you're using memory modules with only 8 chips/module, it's not a big deal to use 4 modules.  And even with higher chip counts, it still WORKS ... it just has a higher likelihood of an occasional "glitch" due to the distorted waveforms.  I really think a lot of "hiccups" that are blamed on Windows (or Linux) are probably due to random memory errors that aren't detected.    MUCH less likely in your case, since you have ECC modules.

... Also, if fault happens because of the address load, the ECC will recover it so there would be only a performance hit. Not reliability problem.

That's correct -- the ECC will automatically correct single-bit errors, which are the most likely thing that will happen if a distorted waveform causes a "glitch"

Thanks again!

You were really helpful!

Just as a note, I ran an Atlhon 5350 as an UnRAID box for a while, it worked fine.  I only changed it because it choked doing Plex Transcoding.  Otherwise it was fine.  I ran a single 8GB stick.

The nice thing about the Athlon was the very low power consumption, it used less power under load than most other machines use idling.