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3
Network Design Criteria
3-13
Fibre Channel End to End CRC
On the FCXL2 adapter board, frame transmission and CRC frame
data integrity are controlled by separate hardware components.
Upon transmission of a Fibre Channel Frame from the buffer memory
to an attached Fibre Channel switch, the FCLX2 transmission
hardware will generate a CRC value based upon the actual data
within the frame. The FCXL2 CRC data integrity hardware will then
insert the CRC value that had been previously verified and
forwarded by the peer FCXL2 hardware into the frame CRC field.
This insures the Frame Level CRC is based upon the frame data that
was present on the ingress FCXL2 adapter. Monitoring of Frame
Level CRC errors will be done at the attached Fibre Channel switch.
Fibre Channel End to End CRC
End-to-End CRC (Cyclic Redundancy Check) support is
automatically enabled for FC/SCSI Tape Pipelining (Device
Extension) configurations under the following conditions.
When powering up or resetting the UltraNet Edge 3000, the FCXL2
Fibre Channel driver will determine if each attached Fibre Channel
PCI card has hardware installed with CRC support. The ON/OFF
status of End-to-End CRC is displayed in the
fcxl2 dump
crc_stats
user interface command.
When an FCP-SCSI I/O with associated data is received, hardware on
the FCXL2 Fibre Channel PCI adapter calculates a CRC value on the
entire I/O data payload. This CRC value is forwarded along with the
I/O and associated data by the FCXL2 Fibre Channel driver to its
peer Fibre Channel PCI adapter.
Upon receipt of the FCP-SCSI I/O to output, the peer FCXL2 Fibre
Channel PCI adapter will again calculate a CRC value on the
outbound data payload. At the completion of the data phase of the
I/O, the FCXL2 Fibre Channel driver will compare the output
hardware calculated CRC with the CRC value forwarded from its
peer. The status phase of the I/O is then based upon the comparison
of the locally generated CRC value with the forwarded CRC value. If
the values match, good ending status is presented during the status
phase of the associated I/O. If the values do not match, bad ending
status is presented during the status phase of the associated I/O.
Monitoring of End-to-End detected CRC errors may be done by
monitoring the counts at
fcxl2 dump crc_stats.