Hi Ceph users! We are currently configuring our new production Ceph cluster and I have some questions regarding Ubuntu and NVMe SSDs. Basic setup: - Ubuntu 18.04 with HWE Kernel 5.3 - Deployment via ceph-ansible (Ceph stable "Nautilus") - 5x Nodes with AMD EPYC 7402P CPUs - 25Gbit/s NICs and switches for Ceph private and public network - 4x Intel P4510 2TB NVMe SSDs (all flash) per Node My questions: 1. Should we deploy more than one OSD per NVMe SSD? (as P4510's performance can sustain e.g. 2 OSDs) 2. Does anyone know NVMe specific Linux settings we should enable? 3. Can we use io_uring, if yes how can we enable it? Is it enough to set bluestore_iouring=true? What I know so far: Ad 1: My opinion is to use at least 2 OSDs per NVMEe SSD as the Intel P4510 is fast enough to serve the parallel requests. Please be aware to use the latest firmware version VDV10170 -> with version VDV10131 we had massive stalls on Ceph side! Ad 2: I have already enabled NVMe polling queues, Ubuntu has disabled them by default: Added nvme.poll_queues=1 to /etc/default/grub, then checked /sys/block/nvme1n1/queue/io_poll Cf. https://lore.kernel.org/linux-block/20190318222133.GA24176@localhost.locald… Ad 3: This commit states it should be possible to use io_uring: https://github.com/ceph/ceph/pull/27392 This issue also shows how to set bluestore_iouring=true but it's not clear if any more setup is required, like liburing: https://github.com/axboe/liburing A presentation from Christoph Hellwig shows the advantages: https://www.snia.org/sites/default/files/SDC/2019/presentations/NVMe/Hellwi… Any help and inputs would be appreciated, THX - Georg