SCSI devices

A SCSI (Small Computer Systems Interface) bus is simply another bus that you can attach multiple peripherals to.

Neutrino supports many brands and varieties of SCSI adapters; see the devb-* (block-oriented) drivers in the Utilities Reference.

When the SCSI driver starts up, it scans the bus for attached devices. When the driver finds a supported device, it creates an entry in the /dev directory (e.g., a hard drive is hdx, where x is the number of the drive, starting from 0).

If the driver doesn't find any devices, it might not know the device ID of the adapter. Passing the device ID and vendor ID to the driver often corrects this problem. On a self-hosted system, you can pass these options to the driver via diskboot; see Controlling How Neutrino Starts.

In the following example, the driver automatically scans for SCSI devices on the chain and adds them into the /dev directory as they're found. For example, if the system has four hard drives in it, the entries in the /dev directory are as follows:

• /dev/hd0—lowest SCSI ID first
• /dev/hd1
• /dev/hd2
• /dev/hd3—the last SCSI hard drive detected

When the driver starts, it sends debugging information to the system log, which you can view using sloginfo. This information is often very helpful when you're trying to debug a problem with a SCSI adapter or device.

If the driver doesn't correctly detect a device, check the following:

• Is the SCSI chain terminated correctly? This is frequently the problem when a device doesn't show up correctly, shows up and then disappears, or doesn't show up at all.
• Is the SCSI adapter supported? Even if an adapter claims to be compatible with a supported adapter, that doesn't mean that the driver will work with it correctly. Compatible doesn't mean identical. To be certain, look for the device ID on our website; see the Community area of our website, http://www.qnx.com.
• Does the SCSI BIOS see all the devices correctly?

  If it does, then all the devices are set up correctly, and don't have any conflicting SCSI IDs. You can also check this by using another operating system; if it detects the devices correctly and doesn't display any problems, the setup is correct.

  Remember that if a SCSI chain isn't terminated correctly, a device may appear on the chain, but will likely have problems after some use. Each device on a SCSI chain needs to have a unique ID number between 1 and the maximum value supported by the adapter (check the user manual for the adapter). If two devices have the same ID, one or both may malfunction or not be recognized by the computer.

• Is there a PCI-bridging problem? Try moving the SCSI card to another PCI slot. Sometimes a PCI-bridging problem can prevent Neutrino from properly attaching to the card. This can happen because Neutrino doesn't support bridges of type "other."
• Is the BIOS set up for a PnP-aware OS? Neutrino isn't a PnP-aware OS.
• Does the adapter or chain need an external power source? If so, even if the device has power, it can't communicate with your computer if the SCSI adapter doesn't have power.
• Check the type of SCSI cable. There are several types, and the type of adapter you're using determines the type of cable you need.

  Also check to make sure that there are no bent pins on the cable. If you're using an adapter to convert between SCSI 2 and SCSI 3, for example, make sure you're using an adapter that's recommended for your hardware. Not all adapters convert the connections correctly.