iser · shipping · also iSER, iSCSI over RDMA

iSCSI Extensions for RDMA (iSER)

iSER extends iSCSI to use an RDMA-capable transport for direct placement of SCSI data into registered I/O buffers.

Related Observatory article: iSCSI Extensions for RDMA (iSER) on hesela.com

Negotiation: RDMAExtensions is session-wide, defaults to No and requires both peers to offer Yes on the leading connection. Discovery sessions cannot negotiate it. Subsequent connections inherit the session's mode. [1]

Transfer direction: The target uses RDMA Write for SCSI-read data and RDMA Read to fetch solicited SCSI-write data. Immediate write data travels with the command in Send, while non-immediate unsolicited data uses Data-Out in Send. [2]

Protection: In iSER-assisted mode, RDMAExtensions=Yes requires HeaderDigest=None and DataDigest=None for every connection in the session and delegates error detection to the RDMA-capable protocol. This does not establish peer authentication, encryption or persistence of a SCSI write. Buffer-access lifetime is a separate concern. [3] [4]

Relations

related

iSCSI, RDMA storage networking, NVMe/RDMA, RDMA steering tag, iSCSI Session, iSCSI digest

Citations

1. RFC 7145: iSER login and RDMAExtensions, sections 5.1 and 6.3 (accessed 2026-10-21)
2. RFC 7145: transfer model and SCSI write operations, sections 1.4 and 9.5.1 (accessed 2026-10-21)
3. RFC 7145: HeaderDigest and DataDigest, section 6.1 (accessed 2026-10-21)
4. RFC 7145: STag invalidation and security considerations, sections 8.3.2 and 11 (accessed 2026-10-21)

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