Remote Direct Memory Access, RDMA for short, makes it possible to send data quickly and easily from a computer’s main storage to the main storage of another computer. This is especially helpful when dealing with large data sets or complex processes, which tend to be required, for example, for machine learning. But what exactly is RDMA and how does it work?
As is the case with the related direct memory access (DMA), one can use remote direct memory access (RDMA) to transfer data directlyfrom a computer’s mainmemoryor working memory to the storage of another computer. In this case, operating systems, CPUs, and cacheare completely ignored so that fewer hardware resources are burdened. For this purpose, the storage transfer with RDMA runs via a private buffer in which the user transfers their data. In doing so, the technology accesses a system’s network cards, where the transfer is processed via Ethernet or InfiniBand.
Remote Direct Memory Access is a technology that has direct memory access as its basis. It enables data to be transferred from a computer’s working memory to the working memory of another system, without burdening the operating systems, cache or CPU in the process.
Many products (hardware and software) already support RDMA. Among these solutions are:
For the data exchange via RDMA to work, a suitable set of protocols in the network cards is required. Typically, TCP/IP is used as a basis. Only through a suitable transport protocol can the technology support so-called zero copy networking, for example. Zero copy networking does not utilize the computer processor. Where both systems enable the use of Remote Direct Memory Access, the data transfer between them is considerably faster than that between systems without RDMA support.
Remote Direct Memory Access is especially helpful in the case of parallel processes on high-performance computers.
For a smooth transfer with RDMA, the following network technologies and interfaces offer the best requirements:
However, Remote Direct Memory Access can also be used in conjunction with Flash or SSD storage mediums and NVDIMMs (non-volatile dual in-line memory modules).
The evolution of RDMA is still in full swing. As with RDMA over Fabrics, its next potential application is already in the starting blocks. Infrastructures between several servers and computers are referred to as a fabric. They support the data transfer via fiber channel networks (storage area networks) and PCI Express (standard for high-speed connections).
One of the main advantages of RDMA is its outstanding speed when compared with other technologies and protocols for data transfer such as iSCSI (SCSI protocol via TCP), fiber channel (FC) or fiber channel over Ethernet (FCoE). However, the final speed of the data exchange also depends on the RDMA variant. Ethernet and InfiniBand are especially popular, as these enable transfer speeds of 10 to 100 Gigabit per second. This is especially suitable for areas of application that require high computing power, such as distributed databases, big data analyzes or applications in data centers.
However, RDMA also has disadvantages when compared with fiber channels, which are still used by many companies. In order to introduce RDMA, companies must arrange high investments, as the technology requires the acquisition of new hardware and protocol components. The costs of Remote Direct Memory Access are thus considerably higher than those for FC or FCoE. In addition, the speedy data transfer via RDMA only works if all systems are supported by the technology.
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