Dell uses RAID by default, warning you that you may not be able to boot into your machine if you try and make the change. I'm not sure the specific reasons they give for doing it this way (if somebody else knows, feel free to chime in) but they say not to do it.
Unless maybe you're doing a clean install of Windows, switching from VMD to AHCI is noticeably less tedious than switching from AHCI to VMD. On modern systems with NVMe, leaving VMD turned on is usually recommended. Not being able to use Samsung Magician to upgrade your SSD firmware is a sacrifice, but there are ways to work around that limitation. I.e., either you can temporarily switch to AHCI (even though switching it back is a bit tedious) or you can use the ISO method from Samsung to upgrade the firmware with it. I don't think that Samsung will be releasing any new firmwares for my Samsung 980 PRO anynore now anyway so, I am probably immune to it.
Using Intel® Volume Management Device (Intel® VMD) on systems without a RAID configuration—often referred to as running in "pass-through" or "single-drive" mode—provides enterprise-level management and reliability features for NVMe SSDs that are typically only available for SAS/SATA drives.
Even without RAID, VMD turns the CPU into the control point for storage, offering the following benefits:
1. Robust "Surprise" Hot-Plug/Hot-Unplug
Safe Removal/Insertion: Allows for the removal or insertion of NVMe SSDs without shutting down or rebooting the server.
Improved Availability: Enables rapid replacement of failed drives in production environments, reducing downtime.
2. Enhanced Error Isolation and Management
Error Handling: VMD separates NVMe SSD error handling from the Operating System.
Reduced System Crashes: If a single NVMe drive experiences a fatal error, VMD helps prevent the entire operating system from crashing or forcing a reboot.
Drive Reliability: Provides enterprise-level reliability, availability, and serviceability (RAS) for NVMe storage.
3. LED Status-Light Management
Visual Indicators: Standardizes LED management for NVMe drives, allowing administrators use management software to visually identify which drive has failed or is in a "safe to remove" state.
Reduced Error Risk: Essential in data centers with high-density storage to ensure the correct drive is replaced, reducing the risk of accidental data loss.
4. Direct Assignment for Virtualization (Direct-to-VM)
Performance Bypass: In virtualized environments (like VMware), VMD allows individual NVMe drives (or a VMD domain) to be assigned directly to a virtual machine.
Lower Latency: This bypasses the hypervisor, offering near-native NVMe speed for VMs.
5. Standardized Management Interface
Uniform Management: Provides a consistent method to manage NVMe drives from various manufacturers using tools like the Intel Virtual RAID on CPU (VROC) driver stack, even without RAID.
6. Performance and power consumption optimizations
Intel VMD optimizes performance and power consumption by acting as an "integrated endpoint" within the CPU's root complex, which fundamentally changes how the OS interacts with storage hardware.
Performance & Interrupt Handling
Compared to the aging AHCI (SATA) protocol, Intel VMD leverages the modern NVMe architecture to handle interrupts more efficiently:
MSI-X Exclusive Support: Intel VMD child devices must use Message Signaled Interrupts eXtended (MSI-X). Unlike AHCI’s traditional shared interrupt lines (INTx) which require the CPU to "poll" every device on a shared line, MSI-X allows each NVMe drive to have its own dedicated, high-priority interrupt vectors.
Parallelism & Scaling: MSI-X supports up to 2,048 independent interrupt vectors per device. VMD uses this to map storage interrupts directly to specific CPU cores, reducing "bottlenecks" during high I/O operations and improving responsiveness in multi-core systems.
Interrupt Remapping: VMD provides hardware-level interrupt remapping, which isolates storage interrupts within its own PCI segment. This prevents a single malfunctioning drive from flooding the entire system with interrupts, preserving overall system stability.
Power Consumption Reductions
VMD enhances power efficiency primarily through more granular control over the PCIe lanes and power states:
Granular Lane Management: Intel VMD allows the system to turn PCIe lanes on or off at x4 granularity. This means if a drive is idle or removed, the specific lanes assigned to it can be completely powered down without affecting other devices on the same physical x16 slot.
L1 Sub-state Support (ASPM): VMD works with Active State Power Management (ASPM) to transition links into deep sleep states like L1.1 and L1.2.
L1.1 (Snooze): Turns off the transceiver PLL while maintaining common-mode voltage.
L1.2 (Off): Shuts down common-mode voltage keepers, reducing idle power consumption by up to 1000x compared to the standard L1 state.
Hardware-Managed Hot-Plug: By managing "surprise" removals at the hardware level, VMD ensures that when a drive is pulled, the PCIe link is immediately and cleanly terminated, preventing wasted power or bus-level hangs from "ghost" devices.
Note on Efficiency: While VMD enables these features, the actual power savings depend on your SSD's firmware supporting these PCI-SIG L1 sub-states.
7. Unified Security & SED Management
Intel VMD allows for Self-Encrypting Drive (SED) Key Management through the Intel VROC framework.
Centralized Authentication: It provides a standardized way to manage encryption keys for SEDs, ensuring that even a single boot drive is secured before the OS loads.
Secure Erasure: VMD-aware drivers simplify the execution of NVMe "Sanitize" commands, allowing you to crypto-erase or block-erase all data on a drive instantly for secure decommissioning.
8. Expanded PCIe Address Space
VMD effectively adds a new PCIe segment for each controller enabled, providing up to 128 additional buses per VMD domain.
Overcoming Bus Limits: This is critical for high-density systems (like servers or workstations) where you might hit the standard 256-bus limit. VMD allows the system to scale to a significantly higher number of NVMe devices without running out of PCIe addresses.
9. Out-of-Band (OOB) Monitoring
VMD enables Out-of-Band Management, allowing administrators to interact with the drive through a Baseboard Management Controller (BMC) even if the OS is not running or has crashed.
Health Checks: You can retrieve drive inventory, temperature, and wear-leveling data remotely.
Predictive Failure: VMD can trigger alerts if a drive's health parameters fall below safe thresholds, allowing for proactive replacement before data loss occurs.
10. Standardized Driver Stack
By using VMD, you consolidate your storage management under a single Intel RST/VMD driver rather than relying on the generic Microsoft NVMe driver.
Consistent Updates: This ensures that all connected drives (regardless of brand) benefit from the same stability patches and performance optimizations provided by Intel's specialized storage team.
