Fibre Channel Protocol support

Edit online

Fibre Channel Protocol (FCP) channels provide for the attachment of SCSI devices using the industry-standard Fibre Channel Protocol for SCSI. Devices can be attached directly to the CPC using point-to-point connections or through a storage area network (SAN). The SAN may consist of any number of switches between the initiator (channel) and target (SCSI device). Switch attachment for targets may also include fibre channel arbitrated loops when supported by the switch. Devices with parallel SCSI interfaces must be attached using fibre-channel-to-SCSI bridges.

A fibre channel is placed in the FCP mode of operation by defining the CHPID as type FCP in the I/O configuration. Unlike FICON channels, the subchannels (IODEVICEs) on an FCP CHPID do not each represent specific remote SCSI devices, but instead define an entry point to a SAN or a communications link to a directly-attached SCSI device. The software uses the subchannel as the initiator of a connection to a remote worldwide port name (WWPN) in order to address a specific SCSI logical unit number (LUN). The remote WWPN and LUN are provided by the software.

An FCP channel path supports a maximum number of valid subchannels. Valid subchannels are devices that are defined to a logical partition and permitted for use by the logical partition. Valid subchannels are calculated as follows:
  • For unshared channel paths, each device defined in IOCP represents a single valid subchannel.
  • For reconfigurable FCP channel paths on CPCs with fixed HSA, each device defined in IOCP represents multiple valid subchannels based on the total number of logical partitions (LPs) in its CHPID candidate list. All CPCs covered by this publication have fixed HSA (see Table 1).
  • For shared channel paths, each device defined in IOCP represents multiple valid subchannels based on the total number of logical partitions (LPs) in its device candidate list.
For example, with a maximum of 480 valid subchannels, if your configuration has 10 LPs and an FCP channel path is shared by all 10 LPs, each device assigned to the shared FCP channel path has a device candidate to all LPs. This design allows you to define a maximum of 48 devices per LP for a total of 480 valid subchannels on the channel path. However, if you specify device candidate lists of 5 LPs for each device on the channel path, this design allows you to define a maximum of 96 devices per LP for a total of 480 valid subchannels.

Unit addresses FE and FF are reserved and cannot be assigned to an FCP subchannel.

FCP channels use the Queued Direct I/O (QDIO) interface and support the QDIO Assist functions of the processor.