A SCSI bus timeout occurs when either the SCSI controller or the SCSI device detects that a command has not been responded to within a specific timeout period. Normally, commands are issued by the SCSI controller, which then waits for a response from the device being addressed. If no response is detected, the controller may reset the bus to reinitiate communication. While disk drives normally recover well from SCSI bus timeouts and resets, tape drives have much greater difficulty in doing so.

To try to detect problems such as these, the architects of the SCSI bus, and Backup Exec (tm) programmers have defined time limits for possible operations being performed by tape drives attached to the SCSI bus. Normally, these timeout values are large enough to accommodate any delay, including retries, in executing the specific command being attempted. In the event that the device does not respond in the amount of time indicated by the timeout value, a timeout occurs.

Usually, the first indication of a timeout is that the tape drive ceases activity. However, because some operations can take several hours on some tape drives, some timeout values are very long, which can make it seem as if the program itself has stopped responding, or that there is an application error of some kind.

Resolution:
Given below are some suggested changes and checks to help resolve the SCSI timeout issue.

First, ensure that the Backup Exec drivers are installed.

1.  Right-click the My Computer icon on the desktop, and then select Manage.

2.  Select Device Manager, and from the right pane, expand Tape drives, right-click the tape device and then select Properties.

3.  Select the Driver tab; ensure a Veritas or Symantec signed driver is listed (Driver Provider).

4.  If the driver is not signed by Veritas or Symantec, execute the Device Configuration Wizard from within the Backup Exec GUI | Tools | Wizards.

5.  Select the Install tape device drivers and follow the wizard to install Symantec drivers for your tape device.

6.  Reboot server and confirm a new driver is loaded.

Second, check configuration on the SCSI controller.

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WARNING: The Parity Checking adjustment is for diagnostic use only and should never be left disabled during production backups. Symantec Corporation cannot be held liable for data corruption due to Parity Checking being disabled.

Hardware Issues:

Additional errors that may be resolved by following this TechNote: