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