The iSCSI Extensions for RDMA (iSER) is a computer

network protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics, and synchronization of ...

that extends the Internet Small Computer System Interface (

iSCSI Internet Small Computer Systems Interface or iSCSI ( ) is an Internet Protocol-based storage networking standard for linking data storage facilities. iSCSI provides block-level access to storage devices by carrying SCSI commands over a TCP/IP ...

) protocol to use Remote Direct Memory Access ( RDMA). RDMA can be provided by: -

Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main communications protocol, protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, th ...

(TCP) with RDMA services (

iWARP iWarp was an experimental parallel supercomputer architecture developed as a joint project by Intel and Carnegie Mellon University. The project started in 1988, as a follow-up to CMU's previous WARP research project, in order to explore building ...

), which uses an existing

Ethernet Ethernet ( ) is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

setup and therefore has lower hardware costs. - RoCE (

RDMA over Converged Ethernet RDMA over Converged Ethernet (RoCE) is a network protocol which allows remote direct memory access (RDMA) over an Ethernet network. There are multiple RoCE versions. RoCE v1 is an Ethernet link layer protocol and hence allows communication between ...

), which does not need the TCP layer and therefore provides lower latency. -

InfiniBand InfiniBand (IB) is a computer networking communications standard used in high-performance computing that features very high throughput and very low latency. It is used for data interconnect both among and within computers. InfiniBand is also used ...

iSER permits data to be transferred directly into and out of

SCSI Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices, best known for its use with storage devices such as hard disk drives. SCSI was introduced ...

computer memory buffers (those which connect computers and storage devices) without intermediate data copies and with minimal

CPU A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary processor in a given computer. Its electronic circuitry executes instructions of a computer program, such as arithmetic, log ...

involvement.

History

An RDMA consortium was announced on May 31, 2002, with a goal of product implementations by 2003. The consortium released their proposal in July, 2003. The protocol specifications were published as drafts in September 2004 in the

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and issued as RFCs in October 2007. The OpenIB Alliance was renamed in 2007 to the

OpenFabrics Alliance The OpenFabrics Alliance is a non-profit organization that promotes remote direct memory access (RDMA) switched fabric technologies for server and storage connectivity. These high-speed data-transport technologies are used in high-performance c ...

, and then released an

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software package.

Description

The motivation for iSER is to use RDMA to avoid unnecessary data copying on the target and initiator. The Datamover Architecture (DA) defines an abstract model in which the movement of data between iSCSI end nodes is logically separated from the rest of the iSCSI protocol; iSER is one Datamover protocol. The interface between iSCSI and the Datamover protocol, iSER in this case, is called Datamover Interface (DI). The main difference between the standard iSCSI and iSCSI over iSER is the execution of SCSI read/write commands. With iSER the target drives all data transfer (with the exception of iSCSI unsolicited data) by issuing RDMA write/read operations, respectively. When the iSCSI layer issues an iSCSI command PDU, it calls the Send_Control primitive, which is part of the DI. The Send_Control primitive sends the STag with the PDU. The iSER layer in the target side notifies the target that the PDU was received with the Control_Notify primitive (which is part of the DI). The target calls the Put_Data or Get_Data primitives (which are part of the DI) to perform an RDMA write/read operation respectively. Then, the target calls the Send_Control primitive to send a response to the initiator. An example is shown in the figures (time progresses from top to bottom). All iSCSI control-type PDUs contain an iSER header, which allows the initiator to advertise the STags that were generated during buffer registration. The target will use the STags later for RDMA read/write operations.

History

Description

See also