Viable DC optane configurations?

[Ouroboros]

I've been looking over the DC optane population guide, but it wasn't clear about the case where you don't have DRAM in all memory channels. It seems to suggest, based on the iMC rules, for App Direct mode at least, that for a single CPU socket, supporting 6 or more memory slots supporting 6 memory channels, you should be able get away with oddball configurations.

For example, a common situation is a single CPU socket with 6 memory channels, in a 2+1+1 memory slot configuration for each iMC (8 memory slots total). If I read the guides correctly, it suggests you can get away with a 2x(Optane+DRAM,Optane,Optane) style configuration, for a max 6 DC optane per CPU socket for a 8 memory slot socket.

Most of the vendor DC optane config guides show minimum at least 1 DRAM module per memory channel (thus all channels active with DRAM), then 1 or more DC optane modules in the secondary memory slots per channel. They don't illustrate a low DRAM count configuration. Has anyone experienced using multiple DC optane when not all memory channels are filled with DRAM? Does that even work?

 

[Evan]

No idea if it works but keep in mind that not populating all 6 channels with regular memory will result in a not insignificant memory performance / bandwidth reduction.

I would have assumed if s system is a candidate for optane usage it’s also needing some memory size and performance ? What use case did you have in mind ?

In the other hand I could have imagined those 8 dimm slot systems could easily have used 6 x ram and 2 x optane but along the lines of what your asking I have no idea if this is viable or performance sensible.

 

[Ouroboros]

6+2 is in the population guide, but my aim is gaining access to more PMEM/NVDIMM/DCPMM, both in total available capacity and in terms of number of devices.

 

[Evan]

I assume the main thing is if you door 4+4 assuming it’s supported on that board you will loose that memory performance.
I am afraid I don’t have and specific experience as all systems I would deploy support 6+6 and that’s the only way I have ever considered it.

 

[Patrick]

I have been editing a massive amount of reviews today. My brain is turning to mush.

One thought I had this weekend was that I needed to do a memory population piece.

You need to have DDR4 DRAM in any channel Optane DCPMM populates. Also, I believe the minimum DDR4 stick size in a DCPMM populated channel is 16GB supported. They told me that 8GB was too small to do the validation on and that they expect in a year or two nobody will use smaller than 32GB.

 

[Evan]

Nobody has used anything but 32gb dimms for a few years excerpt small stand alone systems ?

The issue is and the setup I did was 6 x 32gb rdimm and 6 x 128gb optane dimm to meet the storage demands, lucky the application could live with only 384gb main memory. Ok so the issue is if you want to have more memory than that and decent optane dimm size you need to have the special cpu’s that support 2Tb and 4Tb ram

 

[Ytterbium]

Did anyone ever try Optane with quad rank DIMMs, it seems like my computer doesn't like the mix?