Domain Validation

Domain Validation automatically detects, and if necessary, compensates for hardware that is not performing at the optimal level. It does this by reducing the data transfer rate and bus width. This maintains data integrity, even if data transfers cannot occur at the maximum data transfer rate supported by the adapter. If Domain Validation reduces the transfer rate and the bus width, a message is generated to alert you to the problem.

Domain Validation is automatically enabled for all SCSI devices on the bus, as long as the adapter’s maximum data transfer rate is set to 160 MB/s or higher. See “About the Maximum Data Transfer Rate”, for more information on setting the adapter’s transfer rate.

Domain Validation runs each time the initiator and target devices negotiate the transfer rate and bus width. Events that can cause Domain Validation to run are:

Table 5-1 shows the types of problems that Domain Validation can detect:

When Domain Validation determines that communication with the target device is not possible at the maximum data transfer rate supported by the adapter (Ultra320), it writes a warning message to the /var/adm/syslog.log file. Example 5-2 shows a typical log entry:

Example 5-2 Typical Domain Validation syslog Entry

SCSI Ultra320 0/3/1/1 instance 9: Domain Validation forced SCSI Parameter fallback. Target ID 2 - Currently operating at Ultra160 Wide.

The data transfer rate then “falls back” by one level to a slower setting. Table 5-2 lists the fallback levels for most systems:

	NOTE: The number of entries in Table 5-2 is subject to change. It is provided here to give you an example of how the fallback procedure works.

Domain Validation tests are run on all targets on the SCSI bus, even those targets that do not have Ultra320 capabilities. The starting point in Table 5-2 depends on the parameters that were negotiated for any particular target. Since a SCSI bus can contain up to 15 targets, several different SCSI parameters may be in effect at any one time on the bus, because Domain Validation is running on all of the targets at the same time.

For example, if the parameters originally negotiated during the normal SCSI initiator/target communications are equivalent to Ultra320, but Domain Validation determines that the SCSI bus or the target cannot support that data transfer rate, then Domain Validation falls back to Ultra160. After the fallback, Domain Validation repeats its test. If the bus or target still cannot support the transfer rate, Domain Validation falls back another level, to Ultra2 Wide; then to Ultra2 Narrow, and so forth. As long as failures occur, fallback continues, one level at a time, until the lowest level in Table 5-2 (Asynchronous) is reached. Note that Domain Validation does not generate a fallback warning message such as Example 5-2 each time that it falls back a level, but only when it successfully settles at a level. If a failure occurs at the lowest level, the device is taken offline and a Domain Validation failure message is written to the /var/adm/syslog.log file. For example:

SCSI Ultra320 0/3/1/1 instance 9:
Domain Validation failed, device offline.
Target ID = 2.

Restoring Performance After A Domain Validation Fallback or Failure

First, you must fix the problem with the target hardware that caused the fallback. See Table 5-1 for a listing of the types of problems that Domain Validation can detect.

When you have corrected the problem, use the mptutil -t tgt_reset [target_id] command to restart Domain Validation for the specified target, and restore the negotiated parameters to the highest possible transfer rate and bus width. Then check the /var/adm/syslog.log file for any new fallback warning messages, such as Example 5-2. If the problem is fixed properly and Domain Validation is at the correct level, no new warning messages will be present.

If a device has failed all fallback tests and is offline, follow these steps to restore communication to the target hardware:

1. Fix the problem with the target.

2. Run mptutil with the-t tgt_reset option.

3. Power cycle the target (power off and then power on).

4. Run ioscan without the -k option to restart Domain Validation and renegotiate the parameters for the target.

5. Check /var/adm/syslog.log for any new fallback warning messages.

The absence of new fallback messages indicates that the problem is fixed, and the data transfer rate and bus width are at the correct levels.

	NOTE: 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. This would make the file very large, and more important warning and error messages would not be as easy to see.

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 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.