Nehalem Memory: HELP, I’M LOST!!!

Ever find yourself in a new location staring hopelessly at a map, wondering where you are?  Then to make matters worse, you call someone on your cell phone and can’t describe where you are so they can help? I think we’ve all been there more than once…

Since the Intel Xeon® 5500 processors launched in March, I’ve been getting a bunch of questions (including from the Ask An Expert community [] in the Server Room) about DDR3 memory and how best to configure your server platforms to optimize performance.  Many times, folks are having a hard time just getting the conversation started, so here are a couple of tips to get you going.  The good thing is that DDR3 memory picks up where DDR2 memory leaves off in terms of speed, so you know you’ll be moving forward!

  1. Figure out how much memory you need.  With multi-core CPUs now mainstream in servers, you need enough memory to keep these compute engines fed.  One metric you might look at is “GB per CPU core” or “GB per socket” for your existing servers, and then project your memory requirements from there.

  1. Start with DDR3 1066 memory, as that will deliver a good balance of memory performance and capacity. 

ð        If you need more bandwidth (and willing to give up some capacity), use DDR3 1333

ð        If you need maximum capacity (and willing to give up some bandwidth), use DDR3 800

  1. Match your CPU to your memory speed because the faster memory does require a faster processor.  Check out page 11 of the product brief for the quick reference table.

  1. Wherever possible, fill up as many memory channels as possible, and populate all channels evenly (same type, size and number of DIMMs). 

ð        Most two-socket Xeon® 5500 platforms will have a total of 6 memory channels, so aligning your memory requirements to a multiple of 6 GB will optimize memory performance for most application environments.  

ð        However, you can mix/match memory types if your requirements call for something that is not a multiple of 6.

  1. For Server application environments, always go with ECC supported memory.  Decide between Registered (RDIMM) and Unbuffered DIMMs with ECC (UDIMM ECC).

ð        RDIMM provide greatest flexibility across DIMM sizes and availability

ð        UDIMM ECC provide a lower cost alternative if you are using 1 GB or 2 GB DIMMs

You will still want to check with your system vendor on the specifics, such as memory configurations and DIMM types and options supported for a given server, but hopefully this helps you pointed in the right direction.

If you are still lost, ask me a question on this blog or Ask An Expert in the Server Room.