RDMA (Remote Direct Memory Access)
Terms related to simplyblock
What is RDMA (Remote Direct Memory Access)?
Remote Direct Memory Access (RDMA) is a networking technology that enables direct memory access between servers without involving the operating system or CPU. This method bypasses the traditional network stack, significantly reducing latency and CPU overhead, which makes RDMA highly valuable in high-performance computing (HPC), distributed storage systems, and cloud-native environments that require ultra-fast data transfers.
RDMA is especially important when working with modern storage technologies like NVMe over Fabrics (NVMe-oF), where minimizing latency and maximizing throughput are essential. RDMA allows data to move swiftly across the network, making it a critical component in infrastructures that rely on distributed storage systems and high-speed databases.
How does RDMA work?
RDMA works by allowing one computer to place data directly into the memory of another computer without involving the CPU, cache, or operating system on either side. Traditional networking protocols like TCP/IP require multiple data copies and context switches, adding latency and consuming CPU resources. RDMA removes these bottlenecks, transferring data with minimal system involvement.
In storage environments, RDMA is commonly used to accelerate protocols like NVMe-oF, helping organizations achieve local-disk-level performance over the network. Unlike standard Ethernet TCP-based approaches, RDMA uses specialized network cards and drivers to maintain ultra-low latency and high throughput.
RDMA in distributed storage and NVMe/TCP environments
While RDMA powers some of the highest-performing storage networks, it requires dedicated hardware and complex configuration, which can increase costs and reduce flexibility. This has led to the rise of alternatives like NVMe over TCP (NVMe/TCP), which aim to provide similar performance benefits over standard Ethernet networks without specialized hardware.
At simplyblock, RDMA is part of the conversation when comparing performance optimizations for workloads running on Kubernetes, cloud-native databases like PostgreSQL, and latency-sensitive environments. However, simplyblock prioritizes NVMe/TCP to deliver high-performance storage with greater scalability and simplicity.
RDMA vs. TCP/IP Networking
Before looking at the table, it’s essential to know that RDMA dramatically reduces CPU usage and latency compared to standard TCP/IP networking, but at the cost of hardware complexity.
| Feature | RDMA | TCP/IP Networking |
|---|---|---|
| Latency | Ultra-low (microseconds) | Higher (microseconds to milliseconds) |
| CPU Overhead | Minimal | Higher |
| Hardware Requirements | Specialized NICs (e.g., RoCE) | Standard Ethernet NICs |
| Complexity | High | Low |
| Use Case | HPC, storage acceleration | General networking |
Why is RDMA important in storage?
RDMA is especially valuable in storage because it minimizes the delays involved in moving large volumes of data between nodes. In distributed systems using erasure coding and replication, the ability to transfer data quickly and efficiently across the cluster ensures better application performance and reduces recovery times during node failures.
This makes RDMA particularly useful in environments running intensive workloads such as:
- High-performance transactional databases.
- Large-scale analytics platforms.
- Kubernetes storage with demanding persistent volume needs.
- Cloud storage platforms that prioritize low latency.
NVMe over RDMA (NVMe/RDMA)
NVMe over RDMA (often referred to as NVMe/RDMA or NVMe-oF RDMA) is a transport protocol that combines the speed of NVMe storage with the ultra-low latency of RDMA networks. By transmitting NVMe commands directly over RDMA-enabled fabrics like RoCE (RDMA over Converged Ethernet) or InfiniBand, NVMe/RDMA eliminates the need for CPU involvement in data transfer, allowing near-instantaneous access to remote NVMe drives. This makes NVMe/RDMA a top choice for environments where every microsecond matters, such as high-frequency trading, real-time analytics, and large-scale database clusters. However, deploying NVMe/RDMA requires specialized RDMA-capable hardware and careful network design. As an alternative, solutions like NVMe over TCP (NVMe/TCP) provide similar performance benefits over standard Ethernet infrastructure, reducing complexity and cost while supporting scalability across distributed storage systems. At simplyblock, NVMe/TCP is often preferred for its flexibility, but NVMe/RDMA remains essential in the highest-end performance use cases.
RDMA vs. SPDK and DPDK
RDMA often works alongside other acceleration technologies like SPDK (Storage Performance Development Kit) and DPDK (Data Plane Development Kit). While RDMA handles fast network transport, SPDK accelerates local NVMe storage access, and DPDK optimizes packet processing in user space. Together, they provide end-to-end performance improvements across network and storage layers.
Alternatives to RDMA
For many organizations, RDMA’s complexity and cost are barriers to adoption. Alternatives like NVMe/TCP offer a balance of high performance and simplified infrastructure, leveraging standard Ethernet hardware while delivering competitive results. Simplyblock’s NVMe/TCP solutions are designed to meet these needs, offering scalable, distributed block storage with sub-millisecond latencies without the need for RDMA. Simplyblock, however, also supports NVMe-oF over RDMA.
Related Technologies
To deepen your understanding of storage and networking acceleration, explore:
- Thin Provisioning for efficient storage usage.
- Copy-On-Write (CoW) snapshot strategies.
- iSCSI, a legacy storage protocol.
- RoCE (RDMA over Converged Ethernet), a common RDMA implementation.
- InfiniBand, another RDMA-based networking technology.
By leveraging technologies like RDMA, SPDK, and DPDK, modern storage platforms, including simplyblock, deliver the speed and scalability that today’s data-driven workloads require.