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The factors below also impact the ability to successfully hot-plug NVMe SSDs on PowerEdge servers:

• Form Factor – Hot-plug is only supported on U.2 2.5” form factor NVMe SSDs externally accessible in the

front or rear of the server. PCIe Adapter Card NVMe devices do not support hot-plug.

• Mechanicals – PowerEdge servers are designed with high insertion count connectors on our backplane

designs as well as the NVMe SSDs we use. For hot insertions, the NVMe SSD needs to be fully inserted. For

hot removals, the NVMe SSD needs to be fully removed.

• Number of NVMe SSDs supported - All NVMe U.2 2.5” SSDs are hot pluggable, but only one at a time

should be hot plugged.

• Operational Times – Hot-plug operations are only supported once the operating system has loaded. Hot plug

operations are not supported when the OS is shutting down or in pre-boot.

• Timing – Hot-plug operations should be performed in a timely manner. Removal and insertion should be

completed within 1 second.

We’ve discussed above what hot-plug is and why it is important to users. We will now go into details on the inter-

dependencies of the operating system and BIOS to support hot-plug operations with NVMe SSDs.

For many storage device protocols, such as SAS, SATA, and USB, there is no need for orderly removal operations

provided the data on the drives is not critical for continued operation of the system. For these protocols, surprise

remove will suffice. Many operating systems, NVMe device drivers, and applications may not support surprise removal

of NVMe SSDs.

Operating systems, drivers, and applications have many years of hardening to be able to reliably handle surprise

removal of SAS, SATA, and USB storage devices. In all of these cases, there is a storage controller that acts as an

intermediary between the storage device and the operating system, drivers, and applications. While the drives

themselves are removed, the SAS, SATA, and USB storage controllers that the operating system, drivers, and

applications talk to remain in place and are never removed. These controllers are shown above the hot-plug barrier in

Figure 3.

Figure 3 Storage Controller Hot-Plug Comparison