Domain Validation

Domain Validation provides a way to automatically detect, and if necessary, compensate for hardware that is not performing to the optimal level. It does this by reducing the data transfer rate and bus width. This allows you to have data integrity even if data transfers cannot occur at the maximum data transfer rate supported by the HBA. If Domain Validation does reduce the rate and bus width, a message is generated so that you can correct the problem.

Domain Validation is automatically enabled for all SCSI devices on the bus, as long as you have set the HBA’s maximum data transfer rate to its maximum speed (160 MB/s for the A6829A). See “Maximum Data Transfer Rate”“Maximum Data Transfer Rate” on page 45 for more information on setting the HBA’s transfer rate.

	TIP: If necessary, you can disable Domain Validation—if you want to do diagnostics, for example—by lowering the transfer rate to less than Ultra160 through the commands in the BCH menus (see “Maximum Data Transfer Rate”“Maximum Data Transfer Rate” on page 45).

Domain Validation runs each time the initiator device and target device negotiate the transfer rate and bus width. A few things that can cause this are as follows:

Things that Domain Validation might detect are as follows:

When Domain Validation determines that communication with the target device is not possible at the maximum data transfer rate supported by the HBA (Ultra160), it writes the following warning message to the /var/adm/syslog.log file:

SCSI:Ultra160 SCSI Adapter at hw_path: fallback occurred for
target target_ID. Possible causes are improper termination,
improper cabling, or malfunctioning hardware. Verify the
hardware at the next opportunity.

Later, it “falls back” (lowers the transfer rate and bus width) by one level, according to Table 3-1 “Domain Validation Fallback Levels” below.

	NOTE: The number of entries in Table 3-1 “Domain Validation Fallback Levels” above is subject to change. We are providing it here to give you an example of how the fallback procedure works.

As mentioned earlier, Domain Validation tests are run on all targets on the SCSI bus, even those targets that do not have Ultra160 capabilities. Therefore, the starting point in Table 3-1 “Domain Validation Fallback Levels” depends on the parameters that were negotiated for any particular target. In addition, since a SCSI bus can contain up to 15 targets, different SCSI parameters might be in effect at any one time on the bus (because Domain Validation is running on all of the targets at the same time).

If a fallback does occur and you fix the problem with the target hardware, you need to power cycle (power off and then power on) the target hardware and then run ioscan without the -k option (you can specify any other options, though). This restarts Domain Validation for that target and restores the negotiated parameters to the highest possible transfer rate and bus width. Next, look in the /var/adm/syslog.log file for any new “fallback” warning messages (shown earlier in this section). If the problem was fixed properly and Domain Validation is at the correct level, you will not see any new warning messages.

As an example, if the parameters originally negotiated during the normal SCSI initiator/target communications are equivalent to Ultra160, but Domain Validation determines that the SCSI bus or the target cannot support that data transfer rate, Domain Validation falls back to Ultra2 Wide. Then, Domain Validation repeats its test. If the bus or target still cannot support the transfer rate, Domain Validation falls back another level, to Ultra2 Narrow. As long as failures occur, fallback continues, one level at a time, until the last level in Table 3-1 “Domain Validation Fallback Levels” (Asynchronous) is reached. (Note that a “fallback” warning message—shown earlier in this section—is not generated each time Domain Validation falls back a level, but only when it successfully settles at a level.) If the last level is reached and a failure still occurs, the following message is written to the /var/adm/syslog.log file:

SCSI:Ultra160 SCSI Adapter at hw_path: Error: The domain
validation test for target target_ID determined that
communication may not be possible to this target. Verify the
hardware at the next opportunity.

To be able to restore communication to the target hardware, you must fix the problem with the target, power cycle (power off and then power on) the target, and then run ioscan without the -k option to restart Domain Validation and renegotiate the parameters for that target. Next, you need to check /var/adm/syslog.log for any new “fallback” warning messages. The lack of new “fallback” messages means you successfully fixed the problem, and the data transfer rate and bus width are at the correct levels.

Note that when a Domain Validation test succeeds, no message is written to the /var/adm/syslog.log file. The reason is that this would generate a large volume of messages, especially on a system that is used heavily. Not only would this make the file very large, but the more important warning and error messages would not be easy to see.

In addition, a SCSI selection timeout—when a target device does not respond to selection within a certain length of time—will terminate a Domain Validation test on a target, and the target will be considered to be non-existent. This is so that a bus scan or system boot will not be extended by Domain Validation waiting several times for a target that does not exist.

	NOTE: A Domain Validation test that is terminated for one target does not affect the tests being run on any of the other target devices on the SCSI bus.