Remote direct memory access: Difference between revisions

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{{Short description|Low-level hardware direct memory access}}

In [[computing]], '''remote direct memory access''' ('''RDMA''') is a [[direct memory access]] from the [[main memory|memory]] of one computer into that of another without involving either onecomputer's [[operating system]]. This permits high-throughput, low-[[LatencyNetwork (engineering)latency|latency]] networkingmemory access over a network, which is especially useful in massively parallel [[computer cluster]]s.

== Overview ==

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Both [[Red Hat Enterprise Linux]] and [[Red Hat Enterprise MRG]]<ref>{{cite web|url=https://investors.redhat.com/news-and-events/press-releases/2011/06-23-2011|title=Red Hat Enterprise MRG 2.0 Now Available|accessdate=23 June 2011|url-status=dead|archiveurl=https://web.archive.org/web/20160825215016/https://investors.redhat.com/news-and-events/press-releases/2011/06-23-2011|archivedate=25 August 2016}}</ref> have support for RDMA. Microsoft supports RDMA in [[Windows Server 2012]] via [[Server Message Block|SMB Direct]]. [[VMware ESXi]] also supports RDMA as of 2015.

Common RDMA implementations include the [[Virtual Interface Architecture]], [[RDMA over Converged Ethernet]] (RoCE), [[InfiniBand]], [[Omni-Path]] and, [[iWARP]] and Ultra Ethernet.

== Using RDMA ==

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== Transport types ==

RDMA can transport data reliably or unreliably over the Reliably Connected (RC) and Unreliable Datagram (UD) transport protocols, respectively. The former has the benefit of preserving requests (no requests are lost), while the latter requires fewer queue pairs when handling multiple connections. This is due to the fact that UD is connection-less, allowing a single host to communicate with any other using a single queue.<ref>Storm: a fast transactional dataplane for remote data structures: https://dl.acm.org/doi/pdf/10.1145/3319647.3325827</ref>

== References ==