SCSI Inquiry Times Out on a Tape Changer (291814)


The information in this article applies to:

  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Professional
  • Microsoft Windows NT Server 4.0
  • Microsoft Windows NT Workstation 4.0
This article was previously published under Q291814

SUMMARY

If the IOCTL_CHANGER_MOVE_MEDIUM and IOCTL_SCSI_GET_INQUIRY_DATA commands are issued to a tape changer within a short time period, the inquiry command may time out before it is issued to the device.

MORE INFORMATION

A tape changer consists of a single Small Computer System Interface (SCSI) identification (ID) and one or more logical unit numbers. On tape changers, the tape drive and changer mechanism are on separate logical unit numbers.

When you use untagged SCSI commands, only one command can be processed by a single logical unit number at any one time. Because MOVE_MEDIUM(0XA5) and INQUIRY(0x12) are issued as untagged commands, they can both be processed simultaneously by the changer and tape because they are on separate logical unit numbers.

Some manufacturers have designed their SCSI adapters so that untagged commands must be serialized for each SCSI ID instead of for each logical unit number. This behavior causes the commands to be issued to only one logical unit number at a time. The difference between these two procedures is most apparent on commands that take a long time to complete, including rewinding or changing a tape. If the adapter serializes two tagged SCSI commands, the second command may time out before the command is sent to the target device. Although the issue may appear to occur on the target device, the issue is actually caused by the way the SCSI adapter has implemented support for untagged commands.
Modification Type:MinorLast Reviewed:1/25/2006
Keywords:kb3rdparty kbHardware kbinfo KB291814
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