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phoenix |
Intro
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=====
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This file describes some issues involved when using the "ftape"
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floppy tape device driver that comes with the Linux kernel. This
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document deals with ftape-3.04 and later. Please read the section
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"Changes" for the most striking differences between version 3.04 and
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2.08; the latter was the version of ftape delivered with the kernel
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until kernel version 2.0.30 and 2.1.57. ftape-3.x developed as the
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re-unification of ftape-2.x and zftape. zftape was developed in
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parallel with the stock ftape-2.x driver sharing the same hardware
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support but providing an enhanced file system interface. zftape also
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provided user transparent block-wise on-the-fly compression (regard it
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as a feature or bug of zftape).
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ftape has a home page at
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http://www-math.math.rwth-aachen.de/~LBFM/claus/ftape
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which contains further information about ftape. Please cross check
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this WWW address against the address given (if any) in the MAINTAINERS
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file located in the top level directory of the Linux kernel source
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tree.
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Contents
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========
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A minus 1: Ftape documentation
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A. Changes
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1. Goal
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2. I/O Block Size
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3. Write Access when not at EOD (End Of Data) or BOT (Begin Of Tape)
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4. MTBSF - backspace over file mark and position at its EOT side
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5. Formatting
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6. Interchanging cartridges with other operating systems
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B. Debugging Output
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1. Introduction
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2. Tuning the debugging output
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C. Boot and load time configuration
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1. Setting boot time parameters
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2. Module load time parameters
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3. Ftape boot- and load time options
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4. Example kernel parameter setting
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5. Example module parameter setting
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D. Support and contacts
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*******************************************************************************
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A minus 1. Ftape documentation
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==============================
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Unluckily, the ftape-HOWTO is out of date. This really needs to be
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changed. Up to date documentation as well as recent development
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versions of ftape and useful links to related topics can be found at
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the ftape home page at
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http://www-math.math.rwth-aachen.de/~LBFM/claus/ftape
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*******************************************************************************
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A. Changes
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==========
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1. Goal
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~~~~
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The goal of all that incompatibilities was to give ftape an interface
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that resembles the interface provided by SCSI tape drives as close
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as possible. Thus any Unix backup program that is known to work
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with SCSI tape drives should also work with ftape-3.04 and above.
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The concept of a fixed block size for read/write transfers is
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rather unrelated to this SCSI tape compatibility at the file system
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interface level. It developed out of a feature of zftape, a
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block wise user transparent on-the-fly compression. That compression
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support will not be dropped in future releases for compatibility
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reasons with previous releases of zftape.
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2. I/O Block Size
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~~~~~~~~~~~~~~
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The probably most striking difference between ftape-2.x and
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ftape-3.x with the zftape file system interface is the concept of a
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fixed block size: data must be written to or read from the tape in
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multiples of a fixed block size. The block size defaults to 10k
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which is the default block size of GNU tar. While this is quite
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usual for SCSI tapes (block size of 32k?) and the QIC-150 driver
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`./drivers/char/tpqic02.c' ftape-2.x allowed data to be written in
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arbitrary portions to the tape.
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The block size can be tuned either during kernel configuration or
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at runtime with the MTIOCTOP ioctl using the MTSETBLK operation
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(i.e. do "mt -f /dev/qft0" setblk #BLKSZ). A block size of 0
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switches to variable block size mode i.e. "mt setblk 0" switches
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off the block size restriction. However, this disables zftape's
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built in on-the-fly compression which doesn't work with variable
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block size mode.
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The BLKSZ parameter must be given as a byte count and must be a
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multiple of 32k or 0, i.e. use "mt setblk 32768" to switch to a
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block size of 32k.
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The typical symptom of a block size mismatch is an "invalid
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argument" error message.
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3. Write Access when not at EOD (End Of Data) or BOT (Begin Of Tape)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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zftape (the file system interface of ftape-3.x) denies write access
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to the tape cartridge when it isn't positioned either at BOT or
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EOD. This inconvenience has been introduced as it was reported that
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the former behavior of ftape-2.x which allowed write access at
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arbitrary locations already has caused data loss with some backup
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programs.
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4. MTBSF - backspace over file mark and position at its EOT side
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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ftape-2.x didn't handle the MTBSF tape operation correctly. A MTBSF
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call (i.e. "mt -f /dev/nqft0 bsf #COUNT") should space over #COUNT
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file marks and then position at the EOT tape side of the file
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mark. This has to be taken literally, i.e. "mt -f /dev/nqft0 bsf 1"
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should simply position at the start of the current volume.
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5. Formatting
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~~~~~~~~~~
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ftape-3.x DOES support formatting of floppy tape cartridges. You
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need the `ftformat' program that is shipped with the modules version
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of ftape-3.x. Please get the latest version of ftape from
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ftp://sunsite.unc.edu/pub/Linux/kernel/tapes
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or from the ftape home page at
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http://www-math.math.rwth-aachen.de/~LBFM/claus/ftape
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`ftformat' is contained in the `./contrib/' subdirectory of that
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separate ftape package.
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6. Interchanging cartridges with other operating systems
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The internal emulation of Unix tape device file marks has changed
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completely. ftape-3.x now uses the volume table segment as specified
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by the QIC-40/80/3010/3020/113 standards to emulate file marks. As
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a consequence there is limited support to interchange cartridges
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with other operating systems.
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To be more precise: ftape will detect volumes written by other OS's
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programs and other OS's programs will detect volumes written by
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ftape-3.x.
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However, it isn't possible to extract the data dumped to the tape
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by some MSDOG program with ftape-3.x. This exceeds the scope of a
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kernel device driver. If you need such functionality, then go ahead
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and write a user space utility that is able to do
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that. ftape-3.x/zftape already provides all kernel level support
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necessary to do that.
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*******************************************************************************
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B. Debugging Output
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================
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1. Introduction
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~~~~~~~~~~~~
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The ftape driver can be very noisy in that is can print lots of
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debugging messages to the kernel log files and the system console.
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While this is useful for debugging it might be annoying during
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normal use and enlarges the size of the driver by several kilobytes.
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To reduce the size of the driver you can trim the maximal amount of
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debugging information available during kernel configuration. Please
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refer to the kernel configuration script and its on-line help
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functionality.
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The amount of debugging output maps to the "tracing" boot time
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option and the "ft_tracing" modules option as follows:
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1 + errors (with call-stack dump)
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2 + warnings
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3 + information
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4 + more information
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5 + program flow
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6 + fdc/dma info
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7 + data flow
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8 + everything else
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2. Tuning the debugging output
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To reduce the amount of debugging output printed to the system
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console you can
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i) trim the debugging output at run-time with
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mt -f /dev/nqft0 setdensity #DBGLVL
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where "#DBGLVL" is a number between 0 and 9
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ii) trim the debugging output at module load time with
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insmod ftape.o ft_tracing=#DBGLVL
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Of course, this applies only if you have configured ftape to be
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compiled as a module.
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iii) trim the debugging output during system boot time. Add the
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following to the kernel command line:
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ftape=#DBGLVL,tracing
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Please refer also to the next section if you don't know how to
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set boot time parameters.
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*******************************************************************************
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C. Boot and load time configuration
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================================
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1. Setting boot time parameters
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Assuming that you use lilo, the LI)nux LO)ader, boot time kernel
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parameters can be set by adding a line
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append some_kernel_boot_time_parameter
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to `/etc/lilo.conf' or at real boot time by typing in the options
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at the prompt provided by LILO. I can't give you advice on how to
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specify those parameters with other loaders as I don't use them.
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For ftape, each "some_kernel_boot_time_parameter" looks like
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"ftape=value,option". As an example, the debugging output can be
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increased with
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ftape=4,tracing
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NOTE: the value precedes the option name.
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2. Module load time parameters
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Module parameters can be specified either directly when invoking
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the program 'insmod' at the shell prompt:
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insmod ftape.o ft_tracing=4
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or by editing the file `/etc/modules.conf' in which case they take
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effect each time when the module is loaded with `modprobe' (please
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refer to the modules documentation, i.e. `modules.txt' and the
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respective manual pages). Thus, you should add a line
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options ftape ft_tracing=4
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to `/etc/modules.conf` if you intend to increase the debugging
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output of the driver.
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3. Ftape boot- and load time options
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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i. Controlling the amount of debugging output
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DBGLVL has to be replaced by a number between 0 and 8.
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module | kernel command line
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-----------------------|----------------------
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ft_tracing=DBGLVL | ftape=DBGLVL,tracing
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ii. Hardware setup
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BASE is the base address of your floppy disk controller,
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IRQ and DMA give its interrupt and DMA channel, respectively.
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BOOL is an integer, "0" means "no"; any other value means
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"yes". You don't need to specify anything if connecting your tape
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drive to the standard floppy disk controller. All of these
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values have reasonable defaults. The defaults can be modified
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during kernel configuration, i.e. while running "make config",
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"make menuconfig" or "make xconfig" in the top level directory
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of the Linux kernel source tree. Please refer also to the on
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line documentation provided during that kernel configuration
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process.
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module | kernel command line
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-----------------------|----------------------
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ft_fdc_base=BASE | ftape=BASE,ioport
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ft_fdc_irq=IRQ | ftape=IRQ,irq
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ft_fdc_dma=DMA | ftape=DMA,dma
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ft_probe_fc10=BOOL | ftape=BOOL,fc10
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ft_mach2=BOOL | ftape=BOOL,mach2
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ft_fdc_threshold=THR | ftape=THR,threshold
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ft_fdc_rate_limit=RATE | ftape=RATE,datarate
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4. Example kernel parameter setting
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To configure ftape to probe for a Colorado FC-10/FC-20 controller
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and to increase the amount of debugging output a little bit, add
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the following line to `/etc/lilo.conf':
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append ftape=1,fc10 ftape=4,tracing
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5. Example module parameter setting
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To do the same, but with ftape compiled as a loadable kernel
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module, add the following line to `/etc/modules.conf':
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options ftape ft_probe_fc10=1 ft_tracing=4
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*******************************************************************************
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D. Support and contacts
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====================
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Ftape is distributed under the GNU General Public License. There is
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absolutely no warranty for this software. However, you can reach
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the current maintainer of the ftape package under the email address
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given in the MAINTAINERS file which is located in the top level
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directory of the Linux kernel source tree. There you'll find also
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the relevant mailing list to use as a discussion forum and the web
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page to query for the most recent documentation, related work and
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development versions of ftape.
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LocalWords: ftape Linux zftape http www rwth aachen LBFM claus EOD config
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LocalWords: datarate LocalWords BOT MTBSF EOT HOWTO QIC tpqic menuconfig
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LocalWords: MTIOCTOP MTSETBLK mt dev qft setblk BLKSZ bsf zftape's xconfig
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LocalWords: nqft ftformat ftp sunsite unc edu contrib ft MSDOG fdc
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LocalWords: dma setdensity DBGLVL insmod lilo LI nux ader conf txt
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LocalWords: modprobe IRQ BOOL ioport irq fc mach THR
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