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I'm buying a Plextor PX-AG128M6e SSD in hope that it can be used as VMware ESXi 6.0 datastore. And I have checked the Wikipedia M.2 page, who says there are three options available for the logical device interfaces and command sets used for interfacing with M.2 storage devices,

  • (1) Legacy SATA
  • (2) SATA Express using AHCI
  • (3) SATA Express using NVMe

So I'm curious to know which one the M6e belongs to. Of course Legacy SATA is not, because its maximum transfer speed exceeds 6Gbps. But is it (2) or (3), and how do I know that from the product spec? or by software method?

I think I need to know that because (2) and (3) seems to require different OS driver.

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    Do you know the difference between 2 and 3? – Ramhound Jun 29 '15 at 14:25
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    Main difference should be the "command set" send to hardware, AHCI command set is less effective than NVMe's. Command set is a programming world concept. – Jimm Chen Jun 29 '15 at 14:32
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It appears it uses AHCI not NVMe, if you Google Plextor M6E M2 NVMe you get this article with plenty of details:

Considering that, Plextor didn’t have to think long about what protocol to implement in its PCIe SSD product. To minimize potential incompatibilities, it is designed as a regular PCIe card and uses the AHCI protocol. Although not a very handy and progressive solution, it is guaranteed to work in nearly any computer that has at least one PCIe expansion slot.

Well, the actual product is rather more complex than that. Plextor unified its M6e with a similar PCIe drive designed for an M.2 slot. So the desktop M6e drive is an M.2 card (80x22 mm) mounted on a PCIe -> M.2 adapter. Thus, Plextor offers the M6e in two versions, for PCI Express and M.2 slots, which are in fact one and the same drive.

If you look at this diagram of the Linux IO driver stack it shows that NVMe devices are handled quite differently to other devices and will appear on the system as /dev/nvme#n# when using commands like lsblk. See here for an example.

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