How Fibre Channel is purpose built and engineered to meet the demands of enterprise data centers requiring rock solid reliability, high performance, and scalability was explained in detail at our FCIA webcasts “Inside a Modern Fibre Channel Architecture: Part 1” and “Inside a Modern Fibre Channel Architecture: Part 2.” During these presentations, our expert speakers, Patty Driever, Craig Carlson, Dave Peterson and David Rodgers dove into the inner workings of Fibre Channel. The sessions were highly rated by our audiences. Here are answers to the questions they asked.
Q. Regarding FCP= SCSI, isn’t FCP-4 and such standardized by T10, and that is SCSI? How does that play with the other standards also being “FCP,” instead let’s just call them “FC-NVMe™?” That is rather confusing.
A. The FCP-4 standard describes a protocol for flowing the SCSI device architecture over Fibre Channel….in and of itself it is not the SCSI architecture. Standards like FC-SB-6 transport mode and FC-NVMe-2 are not ‘FCP,’ but they do make use of some aspects of the FCP transport to flow different device architectures over Fibre Channel. Those two standards basically ‘piggyback’ off of portions of FCP that allow them to take advantage of some hardware accelerators built into Fibre Channel HBAs.
Q. Does the OS need to resend the FC command that was flushed with SLER, or is that done by the N_Port without the OS on the HBA?
A. The command is resent at a level below the OS (i.e., at the transport level). As such the OS is unaware of any error detection and recovery.
Q. What determines if Class 2 or Class 3 is used and what do storage devices typically use?
A. Use of Class 2 or Class 3 is determined by the Login protocol, and storage devices typically use Class 3 for data transfers.
Q. How relevant is FC in the NVMe® implementation?
A. How to transport the NVMe upper level protocol (ULP) is specified in the Fibre Channel – Non-Volatile Memory Express – 2 standard (FC-NVMe-2). Since this is a technical presentation, we don’t talk about markets, but NVMe over FC has seen a lot of interest from equipment vendors and customers, especially for use with all flash arrays. The FCIA discussed FC-NVMe in detail in our presentations “What’s New in FC-NVMe-2.”
Q. It was nice to hear about CLASS_2, CLASS_3, CLASS_F It would have been nice to see examples of each Frame type.
A. What distinguishes a frame in one class versus another is primarily in the use of the applicable frame delimiters. Frames using Class 2 use the ‘SoFi2‘ frame delimiter to start the first frame in a sequence, and use the ‘SoFn2‘ frame delimiter for all other frames in the sequence. Even the last frame of the sequence uses the ‘SoFn2‘ frame delimiter, but has the ‘End_Sequence’ F_CTL bit set to a ‘1’. Another distinguishing feature of Class 2 is the required use of the ‘Ack’ frame in response to receipt of each data frame sent in Class 2. The first ‘Ack’ frame uses the ‘SoFi2‘ frame delimiter, and subsequent ‘Ack’ frames in the sequence use the ‘SoFn2‘ frame delimiter, until the last ‘Ack’ frame which uses the ‘EoFt‘ frame delimiter. Class 3 frames use the ‘SoFi3‘ and the ‘SoFn3‘ frame delimiters in a similar manner as described above for Class 2, but the Class 3 protocol does not include an ‘Ack’ response to every data frame. Class F behaves like Class 2, but is used only for switch-to-switch (E_Ports). It uses the ‘SoFf‘ frame delimiter for the first frame in a sequence. If an N_Port receives a frame that uses this delimiter, the N_Port discards it.
Q. What is an R_RDY considered to be?
A. Receiver_Ready (R_RDY) is a Primitive Signal that is defined in the Fibre Channel Framing and Signaling standard (see FC-FS-6).
Q. What are the standard Fabric Services D_ID address numbers?
| FF FC 01h to FF FC FEh | Domain Controllers |
| FF FF F0h | N_Port Controller |
| FF FF F4h | Event Service |
| FF FF F6h | Clock Synchronization Service |
| FF FF FAh | Management Service |
| FF FF FCh | Directory Service |
| FF FF FDh | Fabric Controller |
| FF FF FEh | F_Port Controller |
| FF FF FFh | Broadcast |
Q. Can you share some examples of what FDMI looks like?
A. Fabric-Device Management Interface (FDMI) is a service that is distributed and has additional requirements since an HBA may register information via ports attached to different Switches. See Fibre Channel – Generic Services and Fibre Channel – Switch Fabric standards for FDMI details.
Q. What class (of service) is ELS such as RDP?
A. A Read Diagnostic Parameters (RDP) Extended Link Service (ELS) can be sent using any valid class of service.
Q. It would be nice to have an FC 101 / Primer for new people.
A. We’ve got you covered! Start with this FCIA presentation “Fibre Channel Fundamentals.” You can then get more 101 Fibre Channel content at this Fibre Channel Basics Playlist on the FCIA YouTube Channel.
