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I have 5 old servers, each with single socket CPU, 4 physical cores(8 logical) and 128GB of RAM. I am getting started with mongoDB and plan to deploy MongoDB 4.2.2 on my 5 servers for a lab environment. I installed Virtual Box on each one, and plan to have a high-available installation of MongoDB. After a lot of reading I came up with a design and I'd like to get an opinion on my setup, particularly the shard and replica portion of the cluster.

I have the following:

  • 5 Physical servers(denoted as P1 through P5) each with Virtual Box installed. All the VMs are running Ubuntu 16 Server edition guest OS.
  • 3 Config servers sitting on 3 different VMs on 3 different physical servers. Each config server is allocated 1CPU and 4GB of RAM. Let's call these Conf1_P1 (Config server 1 is sitting on Physical server P1), Conf2_P2, Conf3_P3
  • 2 mongos routers sitting on 2 different VMS on 2 different physical servers. Each Router is allocated 2CPUs and 8GB RAM. Let's call these Router1_P4 and Router2_P5
  • 5 Arbiters sitting on 5 different VMs on 5 different physical servers. Each arbiter is allocated 1 CPU and 2GB of Ram. Let's call these Ar1_P2(Arbiter server 1 is sitting on Physical server P2), AR2_P3, AR3_P4, AR4_P5, AR5_P1
  • 5 shards sitting on 5 different VMs on 5 different physical servers:
    • 3 shards are allocated 2 CPUs, and 8GB of RAM. Let's call these SH1_P1, SH2_P2, SH3_P3.
    • 2 Shards are allocated 1 CPU and 8GB RAM. Let's call these SH4_P4, SH5_P5. These are allocated 1 CPU because the physical server these VMS are sitting on only has 4 physical core, and 2 are already assigned to run Mongo Router.
  • 5 replica members: 1 replica/shard on 5 different VMs, each is assigned 1 CPU and 8GB RAM. Let's call these REP_SH1_P2(the replica for shard 1 is sitting on physical server P2), REP_SH2_P3, REP_SH3_P4, REP_SH4_P5, REP_SH5_P1
  • 1 replica set for the 3 config servers
  • 5 replica set, each with 2 members and 1 arbiter:
    • ReplSet1: SH1_P1, REP_SH1_P2, Ar1_P2
    • ReplSet2: SH2_P2, REP_SH2_P3, Ar2_P3
    • ReplSet3: SH3_P3, REP_SH3_P4, Ar3_P4
    • ReplSet4: SH4_P4, REP_SH4_P5, Ar4_P5
    • ReplSet5: SH5_P5, REP_SH5_P1, Ar5_P1

The summary for each physical server's resources usage is as follow enter image description here

I decided to go with 5 shards to maximize parallelism (horizontal scaling). The choice to have only 2 members in a replica set is due to disk space constrain. What are your thoughts on this particular design? Any concern I should be aware of?

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From comments:

  1. mongoS doesn't need much memory/CPU (or even its own machine) and can be located (installed) on the config servers.
  2. config servers don't need that much memory, even when mongoS is there; 1-2GB is enough.

– JJussi

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