10G networking is strongly recommended for building a Ceph cluster, while 1G networking will work; latency will be pushing on the bounds of being unacceptable and will limit you to the size of nodes you can deploy. A thought should also be given to recovery; in the event of a disk or node failure, large amounts of data will need to be moved around the cluster. Not only will a 1G network be able to provide sufficient performance for this, but normal I/O traffic will be impacted. In the very worst of cases, this may lead to OSDs timing out causing cluster instabilities.

As mentioned, one of the main benefits of 10G networking is the lower latency. Quite often a cluster will never push enough traffic to make full use of the 10G bandwidth; however, the latency improvement is realized, no matter the load on the cluster. The round time trip for a 4k packet over a 10G network might take around 90 microseconds, and the same 4k packet over 1G networking will take over 1 milliseconds. In the tuning section of this book, you will learn that latency has a direct effect on the performance of a storage system, particularly when performing direct or synchronous I/O.

If your OSD node will come equipped with dual NICs, strongly look into a network design that allows you to use them active/active for both transmit and receive. It's wasteful to leave a 10G link in a passive state and will help to lower latency under load.