Hey Rick

 

This all comes down to population rules and what is and isn’t possible with DDR4 memory.

 

The R350 has two memory channels , Channel A consists of A1 & A3 Channel B consists of A2 & A4. With DDR4 the memory is interleaved by “banks”.  The R350 has two banks, one bank is comprised of the two white slots ( A1 and A2 ) the second Bank is the black slots(A3 & A4 ).

 

With DDR 4 you can mix channels but not banks. In other words, the two white slots must be identical to each other as they are interleaved and likewise the two black slots must also be identical to each other. But the channels can be mixed i.e., you can have 16GB (single rank) or a 32GB (dual rank) DIMM in A1 (white slot) and an 8GB (single rank) DIMM in A3 (Black slot) but then channel B must be identical to Channel A i.e.  A2 needs to be the same as A1 and A4 needs to be the same as A3.

 

 

Example of supported configuration

 

 

 

Example below of an Unsupported configuration

 

White slots are not identical to each other, and the black slots are also not identical to each other.

 

 

 

To summarise

 

• Channels can be mixed i.e., they can contain different capacity DIMMS and different rank DIMM’s, but banks need to be identical
• Always populate the white slots with the high-capacity DIMM’s – i.e., in the example above of a supported configuration the 32GB DIMM’s are populated in the white slots A1 and A2, and the lower capacity 8GB DIMMs are populated in the Black slots
• Always make sure the DIMMs are the same technology i.e., we only support DDR4 UDIMMS with the R350 but you can buy RDIMMS and LRDIMMS on other sites. You must make sure that the new DIMMS regardless of rank or capacity are also UDIMMS.

 

Just finally in response to your comment regarding “I see the spec's for the R350 server indicates the max memory with a dual-rank setup is 128Gb whereas the max memory with a single-rank setup is 64Gb”

The memory we sell for the R350 is as follows

DDR4 – 8GB UDIMM – single rank

DDR4 – 16GB UDIMM – single rank

DDR4 – 32GB UDIMM – Dual rank

 

So, if you went with all Dual rank DIMM's you would have to remove the two 8GB DIMM’s currently in the system and install 4 x 32GB DIMM’s which would give you the max supported capacity of 128GB or you could insert 2x32GB DIMMs and keep the remaining 2 x 8GB DIMM’s to give a total capacity of 80GB

Without getting to technical the difference between single rank and dual rank is the amount of DRAM chips on the DIMM, a single rank has 9 DRAM chips, 8 for data and one chip for ECC, with dual rank there’s 18 chips - 9 for each rank.  In general, the more ranks on a DIMM the more capacity they have.

 

 

 

Kind regards

emmet