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Difficulty: HardStorage Devices and Interfaces

A field technician is deploying a workstation for video rendering. The motherboard's primary PCIe 4.0 x16 slot is occupied by a high-end graphics card. The technician installs a passive quad-M.2 PCIe expansion card populated with four identical M.2 NVMe PCIe 4.0 x4 SSDs into a secondary physical PCIe 4.0 x16 slot. Upon booting the operating system, only one of the four installed M.2 drives is detected in Disk Management. Which of the following best explains the cause of this issue and the necessary solution?

  1. The secondary slot lacks PCIe lane bifurcation and provides only x4 electrical lanes from the chipset; the card requires a CPU-connected slot supporting x4x4x4x4 bifurcation or an expansion card with an onboard PCIe bridge chip.Answer
  2. B
    The NVMe storage protocol requires SATA controller emulation; the technician must change the storage controller operation mode in UEFI/BIOS from RAID mode to AHCI mode to enable multi-drive detection.
  3. C
    The installed M.2 NVMe drives use M-key edge connectors; the technician must attach M.2 B-key riser adapters to enable multi-lane PCIe bandwidth over secondary motherboard expansion slots.
  4. D
    The secondary PCIe slot operates in legacy PCIe 3.0 mode; the technician must enable PCIe 4.0 duplexing in UEFI/BIOS to double the available bus bandwidth across the expansion card.

Answer

The secondary expansion slot lacks PCIe lane bifurcation support and only provides four electrical lanes from the chipset. To fix this, the expansion card must be installed in a slot supporting x4x4x4x4 bifurcation, or an expansion card with an onboard PCIe bridge switch chip must be used.
Passive multi-M.2 card adapters pass individual PCIe lanes directly from the slot to each drive connector. Reading all four NVMe SSDs requires either motherboard PCIe slot bifurcation (splitting the x16 slot into x4x4x4x4) or an active expansion card equipped with a hardware PCIe bridge switch chip.

Step-by-Step Solution

1
Analyze the hardware components and symptoms.
A passive quad-M.2 expansion card holding four M.2 NVMe drives (each requiring 4 PCIe lanes, totaling 16 lanes) is installed in a secondary slot where only 1 drive is recognized.
Passive M.2 adapter cards do not contain PCIe switches to multiplex signals; they simply route individual PCIe lanes directly from the slot to each M.2 socket.
2
Identify the requirement for passive multi-M.2 carrier cards.
For four NVMe SSDs to work on a single card without a dedicated PCIe switch chip, the host PCIe slot must support PCIe bifurcation (splitting an x16 link into four independent x4 links, or x4x4x4x4).
If the slot only provides electrical x4 lanes from the chipset or does not support x4x4x4x4 bifurcation, only the first drive directly wired to lanes 1-4 will be detected.
3
Determine the correct resolution.
Relocate the card to a slot that supports PCIe slot bifurcation (x4x4x4x4) or replace the passive card with an active expansion card containing an onboard PCIe bridge switch.
An active switch card can multiplex multiple M.2 NVMe drives over existing PCIe lanes without requiring host motherboard bifurcation.

Key Concept

PCIe lane allocation, M.2 NVMe protocol requirements, and PCIe slot bifurcation
Estimated Time:2m 0s
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Topics

Storage Devices and Interfaces

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