Memory Channel Usage

[merced69]

I am setting up a server to run SQL. Is there any real benefit from filling all 6 memory channels, or would I get the same performance with just 2 sticks, with the same total memory? I am looking at the Xeon 5122.

 

[kanewolf]

Assuming that is a new Xeon gold 5122 -- https://ark.intel.com/products/120475/Intel-Xeon-Gold-5122-Processor-16_5M-Cache-3_60-GHz then YES, you will get significant benefit filling 6 DIMM slots equally. That CPU has a 6 channel memory controller. It can read or write all six DIMMs at once. If you only put two DIMMs in you are cutting the memory bandwidth by 2/3. For a SQL server that would be a huge penalty.

 

[merced69]

Assuming that is a new Xeon gold 5122 -- https://ark.intel.com/products/120475/Intel-Xeon-Gold-5122-Processor-16_5M-Cache-3_60-GHz then YES, you will get significant benefit filling 6 DIMM slots equally. That CPU has a 6 channel memory controller. It can read or write all six DIMMs at once. If you only put two DIMMs in you are cutting the memory bandwidth by 2/3. For a SQL server that would be a huge penalty.

Thank you, yes, a new Xeon gold 5122. That is what I thought, but I am having a hard time finding any stats, or approximations on how much performance real world would be lost if 4 of 6 are filled?

 

[kanewolf]

Assuming that is a new Xeon gold 5122 -- https://ark.intel.com/products/120475/Intel-Xeon-Gold-5122-Processor-16_5M-Cache-3_60-GHz then YES, you will get significant benefit filling 6 DIMM slots equally. That CPU has a 6 channel memory controller. It can read or write all six DIMMs at once. If you only put two DIMMs in you are cutting the memory bandwidth by 2/3. For a SQL server that would be a huge penalty.

Thank you, yes, a new Xeon gold 5122. That is what I thought, but I am having a hard time finding any stats, or approximations on how much performance real world would be lost if 4 of 6 are filled?

Probably because, nobody benchmarks with less than optimal configs. Databases can never have too much RAM or too much memory bandwidth if this is a production system. If it is a test system, then it might not matter as much. BUT if you are trying to benchmark your production system with the test system, you want the same config anyway.