Can I mix 16gb and 8gb ram in HP Z840?

[HPLapUserDV7]

I have a HP Z840 workstation with dual xeons and 64 gb of memory which is evenly divided across both CPUs in 8gb sticks. The 8GB modules are all:

HMA81GR7AFR8N-UH - SK Hynix 1x 8GB DDR4-2400 RDIMM PC4-19200T-R Single Rank x8 Module

I have a stick of compatible 16gb ram (see below) which I bought cheap. I am planning to order 4 more.  Can I take out two stick of the 8gb ram, and put in five sticks of this 16gb ram, to boost the memory from 64gb to 128gb. I want two 8gb stick in another workstation and this would be handy,

SK HYNIX 16GB HMA82GR7MFR8N-UH DDR4-2400 ECC RDIMM 2Rx8 PC4-19200T-R CL17 Server Memory

Otherwise, leaving the 64gb in 8gb modules where they are, can I add a further 4 or 5  of these 16gb modules? 

[SDH]

Looks like you'd be mixing dual and single rank memory.

Try this: Search google for, specifically, z840 memory configuration. View the videos and read the posts. All the answers are right there but it is not simple to mix memory. All slots filled with identical memory is the simple way, if they are memory sticks from HP and approved for that workstation.

[HPLapUserDV7]

Thanks for your post. I hadn't considered that mixing single and dual rank memory would be a potential issue. I only spent £10 on the 16gb stick. It will arrive today and I will see if it works, just adding it to what is there already in whatever is the next slot. Elsewhere I read that sometimes you need to set ram timing in bios when you mix sticks.

[SDH]

Such a BIOS option in the Zx40 family does not exist. 2400 is the fastest the memory can run in a Zx40 but only if its V4 processor is rated to that speed. However, faster more recent same type HP memory for the Zx G4 Xeon workstations can run at the 2400 speed in the Zx40 workstations... they will auto-downgrade themselves to match. That is another option and might even be cheaper but that is a more complex topic.

Attached is the memory page for official HP part numbers for memory from the v34 QuickSpecs... that is what you need to focus on. I know how to translate those CTO option alphanumerics into the HP label number you can see in eBay ads, and below are 3 OEM suppliers. Note the bottom Samsung there has its last right-side label suffix different. That is officially for a server but works in the Zx40 workstations just as well. Here's what would work well as 16GB sticks in all of our Z440/Z640/Z840 workstations (note those all are single rank). Bonus: "1721" means made in 2017, week 21:

See the memory page attached as PDF below. There probably is another page in there showing some added part numbers of interest... the later QuickSpecs are the ones to use, not the early ones because things got updated over time.

[HPLapUserDV7]

I got my 16gb memory stick working. Firstly I tried to place it into bank 9 along side the 8gb stick in bank 1. That gave the dreaded 5 beeps error. After reading here that single and double rank ram may have trouble co-existing, I read elsewhere you can't mix single and double rank RAM in a single channel. So I moved the 8gb stick in bank 1 to bank 10. I placed the 16gb stick into bank 1. Success. I now have 80gb RAM and I can order more of those sticks.

My CPUs are E5-2630v4, which I like because of their relatively low TDP of 85w. 

CPU-Z utility recognised the 8gb sticks as DDR4-2400 (1200Mhz) before and after the new 16gb stick was added. In the timings table there are four entries; 1100Mhz, 1166Mhz, 1200Mhz, and another 1200Mhz with various timings, latencies etc. It looks to be the same for the 8gb and 16gb sticks.

I don't know if I have to change anything, or if I am good to go.

Thanks for the links to HP Z840 specs and mentioning the memory I can use. I notice the SK Hynix 16gb stick you posted is one digit different to my new 16gb (working) stick. Do you know what that difference signifies? BTW, my stick is week 05 / year 2017.

Since you gave me a bunch more 16gb sticks which work in the HP Z840 I can probably get an even cheaper deal. 

[HPLapUserDV7]

Is there any reason not to get larger memory modules if you can get them for a good price? I think it is convenient to leave more ram slots free just in case. For example, I can get two 16gb Hynix modules (compatible) for £30 total, or one 32gb Hynix module (not 100% about compatibility, but right stats) also for £30.

PassMark - SK Hynix HMA84GR7MFR4N-UH 32GB - Price performance comparison (memorybenchmark.net)

If the size of ram in each of the quad channels is not the same, what impact, if any, does this have on performance? Example set up (if I bought a couple of 32gb modules on top of what I have now):

CPU0:

channel 0 1x32gb

channel 1 1x16gb

channel 2 2x8gb

channel 3 2x8gb

CPU1:

channel 0 1x32gb

 channel 1 2x8gb

channel 2 1x8gb

channel 3 1x8gb

[SDH]

Happy to help... it took quite a while to get a good feel for the memory thing.

If you post a pics to include the one that looks a bit different I can check what that means. I think you're fine as long as you stick with dual rank only in that second channel. Note that there are more than 1 channels in each major bank. My understanding is that you can have single and dual rank sticks in one workstation but they can't be mixed in one channel. A "channel" does not equal a "bank".

As said earlier I keep things simple and just use same size and rank and ECC and buffered values in all sockets so I don't need to think too much. Plus, I prefer sticks with the HP label and matching numbers on the right-hand side. Yes, I've used non-HP matching sticks but I know how to match and what OEM codes matter on the left-hand side OEM label. HP also supposedly "bins" their memory to better-than-OEM spec values. Not sure if that is still true.

EDIT: Just saw your followup post.... There is a synergistic value in "Quad Channel" memory performance. Leaving slots empty or mismatching in size reduces that. Look at some of the older HP white papers on memory configuration where they show good/better/best performance and you'll see that what I do always gets "best". Plus, it is easy to remember.

[SDH]

You're buying 2400 memory but the fastest your processors can let that run is 2133. 2400 is the top speed for the Zx40 motherboards if they have the fastest v4 processor(s) in place. Take a look at what you're missing. I'd run a bit hotter if I was you...

...you

...me

Remember that the single thread rating is a good indicator of what you "feel" day in and day out.

Another tip: If you're not running a HP Z Turbo Drive G2 card with a fast modern PCIe4 x4 NVMe M.2 stick as your boot/apps drive then you really are missing out on a major leap in performance on your excellent workstation. I'd recommend a 1TB Samsung 980 Pro in that, or a 1TB WD_ Black SN770. I've seen 3475 MB/s Read/3375 MB/s Write in tuned up Zx40 workstations, with these PCIe4 sticks significantly outperforming 1TB PCIe3 x4 NVMe M.2 sticks on the same Zx40 workstation (unchanged otherwise). We're even using that in the HP ZTD Dual Pro card in the upper primary M.2 socket and a 4GB M.2 stick as the documents drive in the adjacent lower secondary M.2 socket (some have zero other drives in place). To run the ZTD Dual Pro that way you turn bifurcation on in BIOS for the recommended PCIe3 x8 socket (to x4x4) so the system sees 2 x4 M.2 sticks on that x8 pathway.

Worth looking into.

[HPLapUserDV7]

I was looking at benchmarks of other Z840 systems earlier today. It is nice there is an upgrade path, and the memory I got with the system was already DDR4-2400. I bought the system for 3D rendering with blender, stable diffusion with a GPU (to buy) or two. So parallel execution will be helpful.

I already installed a HP Z turbo drive with a 4tb PCIE 3.0 drive. I had already installed on a 4TB hard drive and I used acronis cloning software to transfer the whole install over to nvme. 

Thanks again for your help. I feel like I am getting the hang of this.

[DGroves]

the z820/z840 memory systems are rather complex as each cpu can isolate it's ram from the other or combine it as one large pool each cpu can access using bios settings

you can have single or dual cpu configurations

i confine post this to only one cpu

the single cpu z820 cpu has  8 dimm slots, that access 4 memory banks each memory bank is comprised of two dimm slots and must have dimms of the same rank and dimm layout,.... (dimm layout is the total number of chips that are on the dimm)

mixing low density ram that uses 8 memory modules for 16gb and high density modules that use 4 memory chips for 16gb will cause issues

mixing dimms of the same capacity but different ranks will also not work

these models also support 1.5/1.35 voltage dimms and for higher capacity dimms , LR  "load reduced dimms" are required

there are other things to be aware of such as loading the dimms in the proper order and installing the smallest dimm first and the largest capacity dimms last

these links will prove useful

https://h20331.www2.hp.com/Hpsub/downloads/Z820_Memory_Configurations.pdf

https://www.bhphotovideo.com/lit_files/113022.pdf

https://www.manualslib.com/manual/928210/Hp-Z840-Workstation.html

memory rank, as SDH pointed out this must also match for each memory bank