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:

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:

Note: Under QNX 4, the SCSI drivers didn't support any device that had an ID greater than 6. This isn't a problem under Neutrino.

The maximum rate given for a SCSI device is the maximum theoretical burst interface throughput. Sustained throughput depends on many factors.