Root/Documentation/scsi/scsi.txt

1SCSI subsystem documentation
2============================
3The Linux Documentation Project (LDP) maintains a document describing
4the SCSI subsystem in the Linux kernel (lk) 2.4 series. See:
5http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO . The LDP has single
6and multiple page HTML renderings as well as postscript and pdf.
7It can also be found at:
8http://web.archive.org/web/*/http://www.torque.net/scsi/SCSI-2.4-HOWTO
9
10Notes on using modules in the SCSI subsystem
11============================================
12The scsi support in the linux kernel can be modularized in a number of
13different ways depending upon the needs of the end user. To understand
14your options, we should first define a few terms.
15
16The scsi-core (also known as the "mid level") contains the core of scsi
17support. Without it you can do nothing with any of the other scsi drivers.
18The scsi core support can be a module (scsi_mod.o), or it can be built into
19the kernel. If the core is a module, it must be the first scsi module
20loaded, and if you unload the modules, it will have to be the last one
21unloaded. In practice the modprobe and rmmod commands (and "autoclean")
22will enforce the correct ordering of loading and unloading modules in
23the SCSI subsystem.
24
25The individual upper and lower level drivers can be loaded in any order
26once the scsi core is present in the kernel (either compiled in or loaded
27as a module). The disk driver (sd_mod.o), cdrom driver (sr_mod.o),
28tape driver ** (st.o) and scsi generics driver (sg.o) represent the upper
29level drivers to support the various assorted devices which can be
30controlled. You can for example load the tape driver to use the tape drive,
31and then unload it once you have no further need for the driver (and release
32the associated memory).
33
34The lower level drivers are the ones that support the individual cards that
35are supported for the hardware platform that you are running under. Those
36individual cards are often called Host Bus Adapters (HBAs). For example the
37aic7xxx.o driver is used to control all recent SCSI controller cards from
38Adaptec. Almost all lower level drivers can be built either as modules or
39built into the kernel.
40
41
42** There is a variant of the st driver for controlling OnStream tape
43   devices. Its module name is osst.o .
44
45

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