In a NetApp ONTAP NVMe over Fabrics (NVMe-oF) SAN environment, a subsystem is the construct used to control host access. A subsystem is a collection of one or more namespaces (the NVMe equivalent of LUNs) and a list of authorized host initiators. Hosts are identified by their NVMe Qualified Name (NQN). By adding a host's NQN to the subsystem, you grant that specific host access to the namespaces contained within that subsystem. This is functionally analogous to an initiator group (igroup) in traditional FC or iSCSI environments.

A. igroup: An initiator group (igroup) is used to control host access for SCSI-based protocols like Fibre Channel (FC) and iSCSI, not for the NVMe protocol.

B. Namespace: A namespace is the NVMe equivalent of a LUN. It is the logical block device or storage volume presented to the host, not the object that controls host access.

D. LUN: A Logical Unit Number (LUN) is a construct specific to SCSI-based protocols. The NVMe protocol uses namespaces to represent logical storage units.

1. NetApp ONTAP 9 SAN Administration Guide: In the "NVMe configuration workflow" section

it states

"Create an NVMe subsystem and add hosts to it... An NVMe subsystem is analogous to an iSCSI initiator group (igroup). It specifies which hosts can access the namespaces that are mapped to it." (Search for "NVMe subsystem is analogous" in the ONTAP SAN Administration Guide for your version).

2. NetApp Technical Report TR-4684: NVMe over Fabrics at NetApp: Section "NVMe Subsystems

" states

"In ONTAP

an NVMe subsystem is analogous to an igroup in FC or iSCSI. It is a container for namespaces and defines the hosts that are allowed to access those namespaces." (Page 10).

3. NetApp ONTAP Command Reference Manual: The command vserver nvme subsystem host add is used to "add a host to an NVMe subsystem." The existence and function of this command directly support that subsystems are used to manage the list of hosts.