Nvme

A tri-mode adapter lets any bay take SAS, SATA or NVMe — real flexibility, and the reason U.3 backplanes exist. What it does not advertise is that your NVMe drives stop being NVMe drives: they arrive in Linux as SCSI disks on mpt3sas, queue depth 128, sharing one tag pool and one x8 uplink. Two Gen4 drives saturate the card. A single Gen5 drive is already past it. Whether that trade still makes sense in 2026, and why the universal bays belong to the backplane rather than the controller.

Flash pricing has made all-NVMe hard to justify, and enterprise HDDs are worth another look. Getting acceptable latency out of them on hyper-converged Proxmox Ceph means moving RocksDB off the spindle, pairing each disk with its own Optane through bcache — Optane specifically, because NAND endurance is wrong for that job — and being honest about the failure modes it buys you.

QEMU can emulate a real NVMe controller, so the guest uses its own in-box NVMe driver with no VirtIO media required. It is also unmigratable by design, invisible to Proxmox backups, and no faster than VirtIO SCSI. Here is how to add one and when it is worth it.

512e drives present 512-byte sectors they do not have, and the firmware makes up the difference on every unaligned write. What that costs on the medium, in the host and in write amplification — why direct synchronous writes are the worst case — and how to convert a fleet to 4Kn.

Why PCIe devices lose throughput when passed through to a VM via VFIO, and the practical tuning steps that claw most of it back.