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I have two WD 1T SSDs in my system a SATA 3 and a PCI Express adapter card hosted NVMe. Using 19041 x64 Windows 10, all driver is the default Windows 10.

The NVMe SDD is working properly in NVMe capabilities, 1.6G/s write and 2.3G/s read. However for small 512, 1024, 2048 byte blocks it works approx half speed of the SATA 3 SSD.

I know that for small block way lower performance is expected, but why it is even slower than my SATA 3 SSD? Is this normal, or should I do something?

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    It depends on the type of flash memory used in both devices.
    – Mokubai
    Feb 6, 2021 at 8:19

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This is not entirely surprising.

Flash memories have many subtly different types with different performances, and there are different controllers, with different behaviours and different cache types.

It is entirely possible to have a "Pro" grade SATA 3 SSD that might, for specific use cases, outperform an NVMe SSD.

NMVe is simply the interface. Sure it is a lot faster, but budget parts in a fast case do not change the underlying features of a device.

Many SSDs use multiple flash chips. A well proportioned controller can access these chips more or less simultaneously and achieve high bulk speeds by splitting incoming data across all the devices. When reading it can read from multiple places and again get high speeds.

Small reads and writes will be difficult to speed up and will expose the speed of each individual flash device or sub-unit.

A SATA SSD might have a better flash device or controller built in. It has more space, the design considerations are subtly different, there is more space and scope for heat dissipation, the controller might be clocked higher for some reason. The controllers will also be optimised differently for their particular use cases.

NVMe drives are often designed to score big flashy "3,000 MB/s TRANSFER SPEED" numbers so that they can look good to marketing. That doesn't necessarily mean they are great at the low end as well. Sure those big numbers do help in the majority of cases as well, but as you've seen speed at the high end doesn't always translate to speed at the low end.

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  • Many thx. Can we say that as a Windows 10 boot/system drive, my SATA 3 which outperforms below 4k my NVMe, is at least as good? (so I do not have to worry about how to install Win 10 on the NVMe) Feb 6, 2021 at 8:43
  • Windows might see some benefit to being installed on the NVMe as a lot of booting does involve large transfers. Especially with Windows Fastboot which is essentially a hibernation of the system rather than a real boot - one large transfer. In all honesty though it's not mandatory to move and likely you'd not notice a massive difference between them. It's nowhere near the difference of going from a HDD to an SSD, its a 2 or 3 times difference rather than multiples of 10. I have my boot drive as a relatively slow NVMe drive (~1GB/s) while a faster 2.5GB/s NVMe is used for storage.
    – Mokubai
    Feb 6, 2021 at 8:50
  • OK, many thx again Feb 6, 2021 at 10:57

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