Compare Fibre Channel, iSCSI and FCoE. What should a network engineer know about storage networking?

Block and file

A SAN gives hosts raw block devices (FC, iSCSI, FCoE, NVMe-oF). A NAS shares files (NFS, SMB).

Fibre Channel essentials

• WWNN and WWPN identify nodes and ports, like burned-in MACs. The switch assigns a 24-bit FCID at fabric login.
• Zoning on the switches decides which initiators may talk to which targets. LUN masking on the array decides which volumes a host sees.
• Credits. A port only transmits when the receiver has advertised buffer space, so FC does not drop for congestion. A slow-drain device instead backs up the fabric.
• Two fabrics. Fabric A and fabric B are physically separate and never joined. Hosts use multipathing across them. Cisco MDS adds VSANs to split one physical fabric into logical ones.

iSCSI essentials

• Initiator (host) and target (array), named by IQNs such as iqn.2024-01.com.example:array1.
• TCP 3260, CHAP for authentication, no encryption by default.
• Multipathing across two subnets rather than link aggregation.

FCoE and DCB

FCoE needs PFC (802.1Qbb) for a no-drop class, ETS (802.1Qaz) for bandwidth shares and DCBX to negotiate them. FIP (Ethertype 0x8914) handles discovery and login. It saw use at the server edge and has faded.

NVMe over Fabrics

NVMe/TCP (port 4420) runs on ordinary networks. NVMe over RoCEv2 (UDP 4791) needs a lossless class.