| SCSI subsystem documentation | |
| ============================ | |
| The Linux Documentation Project (LDP) maintains a document describing | |
| the SCSI subsystem in the Linux kernel (lk) 2.4 series. See: | |
| http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO . The LDP has single | |
| and multiple page HTML renderings as well as postscript and pdf. | |
| It can also be found at: | |
| http://web.archive.org/web/*/http://www.torque.net/scsi/SCSI-2.4-HOWTO | |
| Notes on using modules in the SCSI subsystem | |
| ============================================ | |
| The scsi support in the linux kernel can be modularized in a number of | |
| different ways depending upon the needs of the end user. To understand | |
| your options, we should first define a few terms. | |
| The scsi-core (also known as the "mid level") contains the core of scsi | |
| support. Without it you can do nothing with any of the other scsi drivers. | |
| The scsi core support can be a module (scsi_mod.o), or it can be built into | |
| the kernel. If the core is a module, it must be the first scsi module | |
| loaded, and if you unload the modules, it will have to be the last one | |
| unloaded. In practice the modprobe and rmmod commands (and "autoclean") | |
| will enforce the correct ordering of loading and unloading modules in | |
| the SCSI subsystem. | |
| The individual upper and lower level drivers can be loaded in any order | |
| once the scsi core is present in the kernel (either compiled in or loaded | |
| as a module). The disk driver (sd_mod.o), cdrom driver (sr_mod.o), | |
| tape driver ** (st.o) and scsi generics driver (sg.o) represent the upper | |
| level drivers to support the various assorted devices which can be | |
| controlled. You can for example load the tape driver to use the tape drive, | |
| and then unload it once you have no further need for the driver (and release | |
| the associated memory). | |
| The lower level drivers are the ones that support the individual cards that | |
| are supported for the hardware platform that you are running under. Those | |
| individual cards are often called Host Bus Adapters (HBAs). For example the | |
| aic7xxx.o driver is used to control all recent SCSI controller cards from | |
| Adaptec. Almost all lower level drivers can be built either as modules or | |
| built into the kernel. | |
| ** There is a variant of the st driver for controlling OnStream tape | |
| devices. Its module name is osst.o . | |