Processor requirements

Choosing a processor with sufficient capacity is very important. In most cases, the processor is the only component that cannot be replaced once purchased. Its capacity (measured by the number of cores or threads) cannot be scaled up as with the memory or storage. Moreover, the number of central processing unit (CPU) sockets inside a server is always limited. So, in order to get more CPU resources, it is required to either buy higher-end processors, or buy more servers. More servers generate additional costs on their own, require additional space in the data centre and network fabric, and consume more power, so it is usually more economical to choose higher-end processors unless the cost per thread becomes unreasonably high.

Some CPU resources are required for operating system (OS) and control plane services. Different Ceph services have different CPU resource requirements, and so does the Ubuntu OS. For both OS and control plane services, the performance governor should be used, as Ceph benefits from consistently fast CPU performance.

This section outlines CPU requirements for Ceph Object Storage Daemons (OSDs), Ceph Monitors (MONs), the CephFS Metadata Server (MDS), RADOS Gateway (RGW), and the NVMe-oF Gateway service. Read the upstream Ceph documentation to learn more about CPU recommendations.

OSDs

In general, reserving 2 cores per OSD is sufficient. The type of storage device also impacts the number of cores utilised by the OSD. A non-volatile memory express (NVMe) OSD drive can leverage up to 6 cores, which will provide higher input/output operations per second (IOPS) than if fewer cores are available. It is therefore more reliable to consider the desired IOPS and calculate the number of cores required from there. 1 core can provide 1000–3000 IOPS and 200–500 MB/s throughput.

MONs

Ceph MONs are control plane services that are not very CPU-intensive. Resource requirements spike when the cluster is undergoing changes; the Ceph MON service requires 2 to 4 cores to function adequately. For quorum, Ceph MONs should be an odd number.

MDS

Metadata servers are CPU-intensive. They benefit from high clock rate (GHz), and typically only need 2 to 4 cores per MDS.

RGW

RGW requires a minimum of 2 cores. In high-performance scenarios, providing a dedicated server to RADOSGW with 16+ cores will provide better performance.

NVMe-oF Gateway

The Ceph NVMe-oF Gateway service is a CPU-intensive service, and CPU usage grows together with IOPS. In general, separate hosts are strongly preferred for NVMe-oF gateway daemons (or at least isolating them). Provision at least two NVMe-oF gateways in a gateway group, on separate Ceph cluster nodes, for a highly-available Ceph NVMe/TCP solution.

At least 4 CPU cores dedicated to each NVMe-oF gateway instance are highly recommended.

See CPU requirements for a summary of the processor requirements per type of Ceph service.