Troubleshooting
Problem
SCSI device is seen during POST/startup, but not by the operating system for the Servers and IntelliStation.
Resolving The Problem
SCSI device is seen during POST/startup, but not by the operating system
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SCSI device troubleshooting
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When a device attached to the SCSI adapter is not seen by the operating system, there is normally a SCSI device ID or termination issue present.
- First make sure the operating system can see the SCSI adapter. After the driver is loaded for the SCSI adapter, devices attached to it should come available as long as they are configured correctly.
- Without the device driver loaded, the operating system does not have the information required to interface with the adapter. Device drivers are the most likely reason the operating system doesn't see the adapter.
- IBM options usually ship with the drivers on CD or Diskette. If unsure if the adapter or option is compatible with the system, check IBM ServerProven.
- Drivers for IBM options are available at IBM Systems Support.
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If this is an added SCSI adapter and the system already has a SCSI adapter driver loaded, the driver being used may be incompatible with the new adapter.
- It is always suggested to use the most currently tested drivers for any option in a system.
- SCSI termination must be set correctly.
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Termination is always done at the adapter, and at the end of the SCSI chain. The only exception to this is if both Internal and External 16-bit devices are being used off of the same adapter. This causes the adapter to do pass-thru SCSI and Termination is required at both ends of the SCSI chain.
- SCSI adapters have a termination setting within the SCSI Select Utility. The default setting for termination is automatic. It is suggested to leave this setting.
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Determine if the SCSI cable in use is self terminating. To do this, visually inspect the end of the cable for a black block.
- If the black block is present, this is a terminated cable. Now confirm that none of the devices attached to this cable are set to provide termination. Termination cannot be set more than once.
- If the black block is not present, this is not a terminated cable. Now confirm that termination is provided by a device on the SCSI bus. There must only be one device set to terminate, and the terminating device must be connected at the end of the SCSI chain.
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If the SCSI cable is not self terminating, verify if it is 8 bit or 16 bit and terminate the SCSI chain either using a active terminator or on the last device in the chain.
- 16 bit or Wide cabling should be terminated with a 16 bit or wide terminator or device. If a 8 bit terminator is used on a 16 bit cable, only the lower bits will be terminated. This causes the higher bits to bounce along the SCSI cable and can cause SCSI communication problems.
Note: Inspect each SCSI device for the following: ID, damaged connector, power connected, cable, termination
- 16 bit or Wide cabling should be terminated with a 16 bit or wide terminator or device. If a 8 bit terminator is used on a 16 bit cable, only the lower bits will be terminated. This causes the higher bits to bounce along the SCSI cable and can cause SCSI communication problems.
- SCSI ID must be set correctly for all devices on the SCSI chain.
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The SCSI adapter by default is normally set to ID 7. It is suggested to leave this setting at its default and if during troubleshooting find that the ID has been changed, to Load Default Settings of the SCSI adapter which will reset the adapter's ID back to 7.
- The default startup (boot) SCSI ID is 0 for a SCSI hard disk drive.
- An UltraSCSI adapter supports SCSI IDs 0 to 15.
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If you install additional SCSI devices, you must set a unique ID for each SCSI device that you connect to the SCSI cable.
- The SCSI device ID is also known as the SCSI address or physical unit number (PUN).
- This unique ID enables the SCSI adapter to identify the devices and to prevent two devices from sending or receiving data on the SCSI bus at the same time.
- If you install wide (16-bit) SCSI devices, you can set the IDs to any number between 0 and 6, or between 8 and 15. If you install narrow (8-bit) SCSI devices, you can set the IDs to any number between 0 and 6.
- SCSI devices use a variety of methods to set the SCSI ID, such as jumpers, thumbwheels, or switches.
- Use the SCSI Device Utility in the Ctrl+A SCSISelect program to view the SCSI IDs of SCSI devices in the system. (See Using the SCSI Select utility program for more information.)
The SCSI adapter driver is loaded and the operating system sees the SCSI adapter. There are basically two types of SCSI devices. Those that the operating system should immediately find and those that require a device driver to loaded for use. Hard disk drives and tape drives.
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Hard drives
- Hard drives don't require a driver to be loaded however the operating system usually cannot use the drive space without partitioning this space.
- Operating systems have a built in utility to make this space usable. For information on partitioning drive space under a specific operating system, check the help files of that operating system or consult with the operating system manufacturer's website and support personnel.
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Tape drives
- Normally tape drives require a device driver. IBM has a driver available for every tape unit that is available; however, some backup software vendors prepackage drivers into their software. For more information on tape drives, see the following:
If the tip above does not solve the issue, or an IBM component is determined to be faulty, please contact your local IBM Support Center for further troubleshooting or warranty replacement of parts. Please have your Machine Type-Model, serial number, and component Field Replacement Unit (FRU) / Customer Replacement Unit (CRU) part numbers available.
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Document Information
Modified date:
28 January 2019
UID
ibm1MIGR-40571