How to determine how many cores/threads do I need?

yzTyzT Member Posts: 365 ■■■□□□□□□□
My company is going back from the cloud to a local setup. I have designed the architecture already, I'm just missing the server to install the VMs.

I'm considering a few VMs that in overall uses around 40 GB RAM and generally, 2 vCores / VM (except a Docker server that I have assigned 8vCores). Let's say that around 16 vCores.

As the RAM is a fixed value, I know I need to get a server with over 40GB. In fact, I'll go for 64 GB.
However, I'm not sure what kind of processor would I need for this. Do I need to find a processor with 16 threads? Or something with less threads will do the job as well? In other words, does each vCore need a processor's thread?


  • PristonPriston Member Posts: 999 ■■■■□□□□□□
    First, not all cores and CPU are made equally. Some CPU have 8 cores / 16 threads and can handle 50 VMs with 2-4 cores each, while other CPU with the same number of cores can only handle 20 of those same VMs.

    Second, not all VMs use the same amount of CPU. 1 VM that uses alot of CPU can use the same amount of CPU as 20 VMs that don't use much CPU.
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  • dave330idave330i Member Posts: 2,091 ■■■■■■■■■■
    1. CPU vendor - Go with Intel. AMD haven't released a new chipset in a while, so their performance really lags compared to latest Intel chips.

    2. NUMA - Your biggest VM should fit within your NUMA boundary (CPU and RAM). If your biggest VM has 8 vCPU and 64GB of RAM, then the physical server (assuming 2x socket) has to have at least 8 cores/socket and 128GB of RAM.

    3. Cost - Software are typically licensed per socket, so physical CPU should have as many cores/socket as possible. Put together a spreadsheet that include software & hardware cost to see what makes most sense. When software cost goes down, hardware cost goes up. Need to find a balance.

    4. HA - What ever number of servers you come up with, add 1 more for high availability.
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  • tmtextmtex Member Posts: 326 ■■■□□□□□□□
    Just curious, why are they going back to local ?
  • yzTyzT Member Posts: 365 ■■■□□□□□□□
    tmtex, after months researching and testing, the wisest option to do not spend unnecessary money over time is to stay local. Only the HA stuff (the product and some monitoring) will remain in cloud, everything else like code repositories, Jira, Bamboo, etc will move to local.
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