Azure Boost Unleashes 100 Gbps Guest RDMA – Direct Memory Access That Bypasses the CPU Entirely + Video

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Introduction:

Remote Direct Memory Access (RDMA) has long been the secret weapon of high-performance computing, enabling data to move between machines without dragging the CPU and operating system kernel into every transfer. Microsoft has now taken this capability to the next level with the preview of Guest RDMA for Azure Boost, bringing direct, hardware‑offloaded networking straight into guest virtual machines with up to 100 Gb/s of single‑connection throughput. This announcement marks a fundamental shift in cloud networking architecture – one that promises to reshape how AI training, distributed databases, and tightly coupled HPC workloads are deployed in the cloud.

Learning Objectives:

  • Understand the architectural evolution of Azure Boost and how Guest RDMA enables kernel‑bypass networking directly within guest VMs
  • Learn the technical requirements, supported VM families, and operating system configurations needed to enable Guest RDMA
  • Explore practical verification commands and performance tuning techniques for Linux and Windows environments
  • Identify the current preview limitations and understand the roadmap toward general availability
  • Evaluate the security and operational implications of direct NIC‑to‑memory communication in multi‑tenant cloud environments

You Should Know:

  1. Azure Boost and the Guest RDMA Architecture – From Hypervisor to Guest

Azure Boost is Microsoft’s system that offloads server virtualization processes – traditionally performed by the hypervisor and host OS – onto purpose‑built hardware and software. With the general availability of Azure Boost in 2024, VMs could already achieve up to 200 Gbps networking throughput. However, that performance was primarily available at the hypervisor level. Guest RDMA now extends those capabilities into the guest OS itself, allowing applications running inside a VM to directly access the NIC hardware, bypassing the kernel and significantly reducing CPU involvement in packet processing.

The underlying technology is the Microsoft Azure Network Adapter (MANA) – a next‑generation network interface that provides stable forward‑compatible device drivers for both Windows and Linux. MANA is designed with RDMA performance and quality in mind, implemented in FPGA RTL to enable low latency and high throughput. On Linux, the MANA RDMA driver is modeled as an auxiliary device to the Ethernet driver, with hardware exposed as a PCI device supporting multiple network devices over a single PCI function, each optionally exposing an RDMA port.

This architecture delivers three transformative benefits: lower latency and jitter by eliminating kernel traversal, up to 100 Gb/s single‑connection throughput on supported SKUs, and significantly lower CPU overhead – freeing vCPU cycles for actual workload processing rather than networking stack housekeeping.

2. Getting Started – Prerequisites and VM Selection

Before diving into Guest RDMA, you must ensure your environment meets the specific preview requirements. The preview is currently rolling out in the UK South region, with support for direct VM‑to‑VM flows inside the same VNet, including communication across Availability Zones.

Supported VM Families:

The preview works on many D‑series, E‑series, L‑series, FX families, and several network‑optimized SKUs. Specific sizes are documented in the official announcement, so verify your target SKU is included before proceeding.

Operating System Requirements:

  • Ubuntu 24.04 LTS is the recommended Linux distribution
  • rdma‑core >= 50.0 (specifically 50.0‑2ubuntu0.2 or later)
  • Kernel >= 6.8.0 (6.17 is preferred if available)
  • For Windows, appropriate MANA drivers must be installed

Preview Sign‑Up:

Access requires explicit enrollment. You can sign up via the preview link at aka.ms/guestRDMAPreviewSignUp or email [email protected] with feedback.

  1. Linux Configuration – Enabling Guest RDMA Step by Step

Once your VM is provisioned in a supported region with a compatible SKU, follow these steps to enable Guest RDMA on Ubuntu 24.04 LTS:

Step 1: Verify Kernel Version

uname -r

Ensure the output shows `6.8.0` or higher. If you are on an older kernel, update it:

sudo apt update
sudo apt upgrade linux-image-$(uname -r)
sudo reboot

Step 2: Install RDMA Core Packages

sudo apt install rdma-core libibverbs-dev librdmacm-dev

Verify the installation:

rdma --version

Expected output should show version 50.0 or later.

Step 3: Verify MANA Device Detection

The MANA network adapter should appear as a PCI device. Check with:

lspci | grep -i mana

You should see a Microsoft Azure Network Adapter entry.

Step 4: Check RDMA Device Availability

ibv_devinfo

This command lists available RDMA devices. Look for a MANA‑related device with port state ACTIVE.

Step 5: Verify RDMA Capabilities on the Network Interface

rdma link show

This confirms that RDMA is enabled on the network link.

Step 6: Test RDMA Connectivity Between VMs

Using the `ib_write_bw` and `ib_read_bw` benchmarks from the perftest package:

sudo apt install perftest
 On the server VM:
ib_write_bw -a -F
 On the client VM (replace <server_ip>):
ib_write_bw -a -F <server_ip>

These tests measure bidirectional RDMA write and read throughput, which should approach the advertised 100 Gb/s on supported SKUs.

4. Windows Configuration – Enabling Guest RDMA

For Windows VMs, the process involves installing the MANA drivers and configuring the network adapter for RDMA:

Step 1: Install MANA Drivers

Download and install the latest MANA drivers from the Azure documentation or via Windows Update. Verify installation in Device Manager under “Network adapters” – you should see “Microsoft Azure Network Adapter (MANA)”.

Step 2: Enable RDMA on the Adapter

Open PowerShell as Administrator and run:

Get-1etAdapterRDMA

This lists adapters with RDMA capabilities. If RDMA is not enabled:

Enable-1etAdapterRDMA -1ame "Ethernet"  Replace with actual adapter name

Step 3: Verify RDMA Functionality

Get-1etAdapterRDMA | fl

Check that the “Enabled” property is `True` and the “RDMA Capable” property shows True.

Step 4: Test with SMB Direct

SMB Direct leverages RDMA for high‑performance file transfers. On the server:

Set-SmbServerConfiguration -EnableSMB2Protocol $true -EnableSMBDirect $true

On the client, map a drive and test large file transfers – throughput should reflect RDMA acceleration.

5. Performance Tuning and Benchmarking

Achieving the full 100 Gb/s potential requires careful tuning beyond simply enabling RDMA. Microsoft recommends benchmarking and testing workloads to achieve expected network performance.

Linux Tuning Parameters:

  • IRQ Affinity: Pin network interrupt requests to specific CPU cores to reduce latency 
    sudo cat /proc/irq//smp_affinity
  • CPU Governor: Set to `performance` mode 
    sudo cpupower frequency-set -g performance
  • Jumbo Frames: Enable MTU 9000 on the RDMA interface if the underlying network supports it 
    sudo ip link set dev eth0 mtu 9000

Windows Tuning Parameters:

  • RSS (Receive Side Scaling): Enable and configure RSS to distribute network processing across multiple cores 
    Set-1etAdapterRss -1ame "Ethernet" -Enabled $true
  • Interrupt Moderation: Disable or reduce interrupt moderation for latency‑sensitive workloads 
    Set-1etAdapterAdvancedProperty -1ame "Ethernet" -RegistryKeyword "InterruptModeration" -RegistryValue "0"

Benchmarking Tools:

  • Linux: ib_write_bw, ib_read_bw, `qperf` for RDMA latency and throughput measurements
  • Windows: `NTttcp` with RDMA support, or SMB Direct performance counters

6. Current Preview Limitations and Roadmap

While powerful, the Guest RDMA preview comes with notable constraints that you must plan around:

  • No support for load balancers – traffic must be direct VM‑to‑VM within the same VNet
  • No private endpoint support – RDMA flows cannot traverse Azure Private Link
  • No VNet encryption – traffic is not encrypted at the network layer in this preview
  • No flow logging – you cannot log RDMA traffic flows through Azure Network Watcher
  • No User‑Defined Routes (UDRs) – custom routing is not supported
  • No IP forwarding – VMs cannot act as routers for RDMA traffic

These limitations are planned for resolution in the general availability release. For now, treat Guest RDMA as a solution for isolated, high‑performance workloads within a single VNet, rather than a drop‑in replacement for all networking scenarios.

Security Considerations:

Direct memory access between machines raises important security questions. In Azure’s multi‑tenant environment, RDMA is isolated per VM and tenant; the MANA hardware enforces memory registration and access controls. However, since VNet encryption is not yet supported, sensitive workloads should implement application‑layer encryption. Microsoft provides the preview “AS‑IS” and excludes it from service level agreements and limited warranty, so production deployments should wait for GA.

What Undercode Say:

  • Key Takeaway 1: Guest RDMA for Azure Boost represents a paradigm shift in cloud networking – moving from CPU‑centric packet processing to hardware‑offloaded, direct memory access that fundamentally changes the performance profile of distributed applications. This isn’t just an incremental improvement; it’s a re‑architecture of how VMs communicate in the cloud.

  • Key Takeaway 2: The preview limitations are significant but not deal‑breakers for the right use cases. AI training clusters, distributed databases, and HPC workloads that operate within a single VNet can immediately benefit from the 100 Gb/s throughput and microsecond‑level latency. Organizations should identify these specific workloads and begin experimenting now to build expertise before GA.

The introduction of Guest RDMA also signals Microsoft’s broader strategy with Azure Boost: systematically offloading every possible virtualization overhead to purpose‑built hardware. This mirrors trends in the broader industry – from SmartNICs to DPUs – where the cloud provider takes on more of the infrastructure burden to deliver bare‑metal performance with VM flexibility. For cloud architects, this means rethinking application design: workloads that were previously distributed across many smaller VMs to achieve aggregate throughput can now be consolidated onto fewer, larger VMs with direct RDMA communication, potentially simplifying architecture and reducing costs.

However, the security model deserves close attention. Direct memory access across VMs, even within the same tenant, introduces new attack surfaces if not properly isolated. Microsoft’s use of hardware‑enforced memory registration and per‑VM isolation is encouraging, but security teams should validate these controls and consider additional encryption layers for sensitive data. The lack of VNet encryption in preview is a temporary gap, but one that highlights the tension between performance and security – a tension that will require careful trade‑off decisions in production deployments.

Prediction:

  • +1 Guest RDMA will accelerate the adoption of GPU‑accelerated AI workloads in Azure, enabling more efficient distributed training across multiple VMs with GPU Direct RDMA – reducing training times and costs for large language models and computer vision applications.

  • +1 The technology will drive a new class of cloud‑native applications that assume RDMA as a baseline networking capability, much like how accelerated networking became the default over time. This will spur innovation in distributed databases and in‑memory computing platforms.

  • -1 The preview’s limited regional availability (starting only in UK South) creates a geographical bottleneck that may slow adoption for organizations with primary deployments in other regions, potentially delaying the technology’s impact on global workloads.

  • -1 Without VNet encryption and flow logging at launch, security‑conscious enterprises in regulated industries (finance, healthcare, government) may hesitate to adopt Guest RDMA for production workloads even after GA, unless Microsoft addresses these gaps comprehensively.

  • +1 The success of Guest RDMA will likely pressure other cloud providers (AWS, GCP) to accelerate their own RDMA and hardware‑offload roadmaps, leading to a broader industry shift toward hyper‑performance cloud networking over the next 18–24 months.

  • -1 The complexity of tuning and validating RDMA performance – including kernel versions, driver compatibility, and network topology considerations – will create a significant operational burden for teams without deep networking expertise, potentially limiting adoption to specialized HPC and AI engineering groups.

  • +1 As Azure Boost continues to evolve, we can expect further offloads – storage, security, and management functions – all moving into hardware, progressively narrowing the performance gap between cloud VMs and on‑premises bare metal, ultimately making the cloud the default choice for even the most performance‑sensitive workloads.

▶️ Related Video (76% Match):

https://www.youtube.com/watch?v=1MQj-UK2rrY

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