IBM Midrange System DS4000 Series Hardware Manual page 466

Link status
If you experience problems with connectivity or performance or you see entries from RDAC or
the HBA driver in Windows, use the Link Status tab (Figure 7-83) to narrow down the device
causing problems (faulty cable, SFPs, and so on).
Figure 7-83 Link Status tab
The following information can be retrieved from the Link Status window:
Link failure: The number of times that the link failed. A link failure is a possible cause for a
timeout (see the Windows Event Log).
Loss of sync: The number of times that the adapter had to re-synchronize the link.
Loss signal: The number of times the signal was lost (dropped and re-connected).
Invalid CRC: The number of cyclic redundancy check (CRC) errors that were detected by
the device.
Diagnostics
You can use the Diagnostics tab (Figure 7-84 on page 449) to perform loopback and
read/write buffer tests:
The loopback test is internal to the adapter. The test evaluates the Fibre Channel loop
stability and error rate. The test transmits and receives (loops back) the specified data and
checks for frame CRC, disparity, and length errors.
The read/write buffer test sends data through the SCSI Write Buffer command to a target
device, reads the data back through the SCSI Read Buffer command, and compares the
data for errors. The test also compares the link status of the device before and after the
read/write buffer test. If errors occur, the test indicates a broken or unreliable link between
the adapter and the device.
448
IBM Midrange System Storage Hardware Guide