What is RDMA? How does it work?

Today I have brought a topic on technology in which I have written an article about RDMA programming today in which I will give information on how RDMA works, so read the full article.

Remote direct memory access (RDMA) technology increases the speed of server -to- server data movement through better utilisation of networks infrastructure without CPU intervention .the network adapter transfers data directly to or from the application memory without interrupting other parallel operations of the system .RDMA technology is widely used in enterprise data centers and high performance computer (HPC) because of its high-throughput and low latency networking .

This article will enable app developers to start programing RDMA apps even with it.before we start let’s have a brief introduction to Infiniband (Ib) fabric -its features and components.

Infiniband (ib):infiniband is an open industry -standard specification for data flow between server I/O and inter -server communication .ib supports RDMA and pffers high-speed ,low latency ,low CPU overhead ,high efficiency and scalability .the transfer speed infifniband ranges from 10Gbps(SDR) to 56 Gbps (FDR)per port.

Components of infiniband:host channel adapter (HCA)this is provides and address translation mechanism under the control of the operating system ,which allows an application to access the HCA  directly the same address translation mechanism is the means by which an HCA access memory on behalf of a user level application .the application refers to virtual address ,while the HCA has the ability to translate these address into physical address in order to effect the actual message transfer.

Switches Ib:switches are conceptually similar to standard networking switches but are designed to meet Ib performance requirements. They implement the flow control of the Ib link layer to prevent packet dropping and to avoid congestion .they also have adaptive routing capabilities and advanced quality of service .many switches included a subnet manger at least one of which is required to configure an Ib fabric .

Range extenders:infiniband range extension is accomplished by encapsulating the infiniband traffic onto the WAN link and extending sufficient buffer credits to ensure full bandwidth across the WAN.

Subnet managers:the Ib subnet manager is based on the concept of software defined networking (SDN),which eliminates interconnect complexity and enables the creation of very large scale computer and storage infrastructures .the Ib subnet manger assigns local identifiers (LIDs) to each port connected to the infiniband fabric, and develops a routing table based on the assigned LIDs.

How RDMA works:RDMA enables more direct data movement in and out of a server by implementing a transport protocol in the network interface card (NIC) hardware. The technology supports a feature called zero-copy networking that makes it possible to read data directly from the main memory of one computer and write that data directly to the main memory of another computer.

If both the sending and receiving devices support RDMA, then the conversation between the two will complete much quicker than comparable non-RDMA network systems.

RDMA has proven useful in applications that require fast and massive parallel high-performance computing (HPC) clusters and data center networks. It is particularly useful when analyzing big data, in supercomputing environments that process applications, and for machine learning that requires the absolutely lowest latencies and highest transfer rates. You can also find RDMA used in connections between nodes in compute clusters and with latency-sensitive database workloads.