SCSI Devices

SCSI Devices

If the SCSI is the first device you are adding to the host adapter, you need to configure that host adapter into the system. If you are adding a second host adapter (or anything after that), you will have to disable the BIOS on it. Remember from our discussion on SCSI in the chapter on hardware that the system will look for a bootable hard disk. If the BIOS on the second host adapter is enabled, the system may try to boot from this one. If it is the same model host adapter, it will probably have to change the base address, IRQ, and DMA as well.

Remember that every device on the SCSI bus, including the host adapter itself, is identified by a SCSI ID. SCSI IDs range from 7 on standard SCSI and 15 on a Wide SCSI bus. Regardless of what type it is, the host adapter is almost exclusively set to ID 7. It is this ID that is used to identify devices on the bus, not their location in relation to the host adapter.

Because there is typically no real need to configure a SCSI host adapter unless something is attached, the only “official” way to add a host adapter to the system is to go through the configure script. If the system recognizes that you do not have a configured host adapter, you will be prompted to add one.

If you are adding a device to an existing host adapter, the driver for that host adapter is already linked into the kernel. (At least we hope so.) If you are adding new kind of device onto the new host adapter, the driver may not be configured. Watch carefully as the system boots to see whether the device is recognized. If it is not, you will need to run the configure script.

Here is one example in which I have first hand experience about not paying attention to what is supported and what is not. The distribution you have may provide a disk image that has support for a particular host adapter (or any driver for that matter). However, this does not mean the kernel has the support.