Actual speed when using NVMe SSD in NAS: Is it worth the advertisement?

[RoseBL]

Hello everyone, I am planning to buy a NAS with a slot that supports NVMe SSD for cache or primary storage. The manufacturer offers very high read/write speeds (e.g.,3,500 MB/s), but I want to ask from practical experience:

With popular NVMe SSDs like Samsung 970 Evo Plus or WD Black SN750, what percentage of the actual speed when running on the NAS will be compared to the manufacturer's advertised specifications?

What factors have the strongest influence on speed reduction (e.g., NAS motherboard type, network protocol, RAID configuration, firmware)

Are there any NAS that support NVMe SSDs well to maximize their performance? If so, give me some examples to compare.

Thanks, everyone, for sharing in advance!

[ed]

Great question, and one that comes up a lot when people see those big 3,500 MB/s numbers in SSD marketing. In practice, you will not see those speeds on a NAS the way you would in a local PC benchmark.

A few key points:
1. Network bottleneck – Even a 10GbE network link caps out at about 1,100 MB/s real throughput, so that’s your ceiling unless you’re running multiple aggregated 10GbE links or 25/40GbE hardware. On a 2.5GbE or 1GbE NAS, the maximum you’ll see is ~280 MB/s or ~110 MB/s, regardless of whether you use NVMe.
2. NAS motherboard and PCIe lanes – Many NAS models don’t give NVMe drives the full PCIe 3.0 x4 bandwidth. Often, the slot is limited to PCIe 3.0 x2 or even x1, which reduces maximum speed to around 1,600 MB/s or 800 MB/s before other overheads.
3. RAID and firmware overhead – If you run NVMe in RAID or as a cache, the CPU and storage controller add latency. Cache is most useful for small random reads/writes (like databases or lots of small files) rather than large sequential transfers. For video editing or big file moves, the benefit is limited.
4. Real-world results – In most NAS setups, even high-end models, you’ll realistically see 800–1,200 MB/s from NVMe in best conditions, which is about a third of the advertised peak. That’s already very good, but it’s not “3,500 MB/s” as the packaging might suggest.