linux-libre/Documentation/scsi/osst.txt

README file for the osst driver
===============================
(w) Kurt Garloff <garloff@suse.de> 12/2000

This file describes the osst driver as of version 0.8.x/0.9.x, the released
version of the osst driver.
It is intended to help advanced users to understand the role of osst and to
get them started using (and maybe debugging) it.
It won't address issues like "How do I compile a kernel?" or "How do I load
a module?", as these are too basic.
Once the OnStream got merged into the official kernel, the distro makers
will provide the OnStream support for those who are not familiar with
hacking their kernels.


Purpose
-------
The osst driver was developed, because the standard SCSI tape driver in
Linux, st, does not support the OnStream SC-x0 SCSI tape. The st is not to
blame for that, as the OnStream tape drives do not support the standard SCSI
command set for Serial Access Storage Devices (SASDs), which basically
corresponds to the QIC-157 spec.
Nevertheless, the OnStream tapes are nice pieces of hardware and therefore
the osst driver has been written to make these tape devs supported by Linux.
The driver is free software. It's released under the GNU GPL and planned to
be integrated into the mainstream kernel.


Implementation
--------------
The osst is a new high-level SCSI driver, just like st, sr, sd and sg. It
can be compiled into the kernel or loaded as a module.
As it represents a new device, it got assigned a new device node: /dev/osstX
are character devices with major no 206 and minor numbers like the /dev/stX
devices. If those are not present, you may create them by calling
Makedevs.sh as root (see below).
The driver started being a copy of st and as such, the osst devices'
behavior looks very much the same as st to the userspace applications.


History
-------
In the first place, osst shared its identity very much with st. That meant
that it used the same kernel structures and the same device node as st.
So you could only have either of them being present in the kernel. This has
been fixed by registering an own device, now.
st and osst can coexist, each only accessing the devices it can support by
themselves.


Installation
------------
osst got integrated into the linux kernel. Select it during kernel
configuration as module or compile statically into the kernel.
Compile your kernel and install the modules.

Now, your osst driver is inside the kernel or available as a module,
depending on your choice during kernel config. You may still need to create
the device nodes by calling the Makedevs.sh script (see below) manually.

To load your module, you may use the command 
modprobe osst
as root. dmesg should show you, whether your OnStream tapes have been
recognized.

If you want to have the module autoloaded on access to /dev/osst, you may
add something like
alias char-major-206 osst
to a file under /etc/modprobe.d/ directory.

You may find it convenient to create a symbolic link 
ln -s nosst0 /dev/tape
to make programs assuming a default name of /dev/tape more convenient to
use.

The device nodes for osst have to be created. Use the Makedevs.sh script
attached to this file.


Using it
--------
You may use the OnStream tape driver with your standard backup software,
which may be tar, cpio, amanda, arkeia, BRU, Lone Tar, ...
by specifying /dev/(n)osst0 as the tape device to use or using the above
symlink trick. The IOCTLs to control tape operation are also mostly
supported and you may try the mt (or mt_st) program to jump between
filemarks, eject the tape, ...

There's one limitation: You need to use a block size of 32kB.

(This limitation is worked on and will be fixed in version 0.8.8 of
 this driver.)

If you just want to get started with standard software, here is an example
for creating and restoring a full backup:
# Backup
tar cvf - / --exclude /proc | buffer -s 32k -m 24M -B -t -o /dev/nosst0
# Restore
buffer -s 32k -m 8M -B -t -i /dev/osst0 | tar xvf - -C /

The buffer command has been used to buffer the data before it goes to the
tape (or the file system) in order to smooth out the data stream and prevent
the tape from needing to stop and rewind. The OnStream does have an internal
buffer and a variable speed which help this, but especially on writing, the
buffering still proves useful in most cases. It also pads the data to
guarantees the block size of 32k. (Otherwise you may pass the -b64 option to
tar.)
Expect something like 1.8MB/s for the SC-x0 drives and 0.9MB/s for the DI-30.
The USB drive will give you about 0.7MB/s.
On a fast machine, you may profit from software data compression (z flag for
tar).


USB and IDE
-----------
Via the SCSI emulation layers usb-storage and ide-scsi, you can also use the
osst driver to drive the USB-30 and the DI-30 drives. (Unfortunately, there
is no such layer for the parallel port, otherwise the DP-30 would work as
well.) For the USB support, you need the latest 2.4.0-test kernels and the 
latest usb-storage driver from 
http://www.linux-usb.org/
http://sourceforge.net/cvs/?group_id=3581

Note that the ide-tape driver as of 1.16f uses a slightly outdated on-tape
format and therefore is not completely interoperable with osst tapes.

The ADR-x0 line is fully SCSI-2 compliant and is supported by st, not osst.
The on-tape format is supposed to be compatible with the one used by osst.


Feedback and updates
--------------------
The driver development is coordinated through a mailing list
<osst@linux1.onstream.nl>
a CVS repository and some web pages. 
The tester's pages which contain recent news and updated drivers to download
can be found on
http://sourceforge.net/projects/osst/

If you find any problems, please have a look at the tester's page in order
to see whether the problem is already known and solved. Otherwise, please
report it to the mailing list. Your feedback is welcome. (This holds also
for reports of successful usage, of course.) 
In case of trouble, please do always provide the following info:
* driver and kernel version used (see syslog)
* driver messages (syslog)
* SCSI config and OnStream Firmware (/proc/scsi/scsi)
* description of error. Is it reproducible?
* software and commands used

You may subscribe to the mailing list, BTW, it's a majordomo list.


Status
------
0.8.0 was the first widespread BETA release. Since then a lot of reports
have been sent, but mostly reported success or only minor trouble.
All the issues have been addressed.
Check the web pages for more info about the current developments.
0.9.x is the tree for the 2.3/2.4 kernel.


Acknowledgments
----------------
The driver has been started by making a copy of Kai Makisara's st driver.
Most of the development has been done by Willem Riede. The presence of the
userspace program osg (onstreamsg) from Terry Hardie has been rather
helpful. The same holds for Gadi Oxman's ide-tape support for the DI-30.
I did add some patches to those drivers as well and coordinated things a
little bit. 
Note that most of them did mostly spend their spare time for the creation of
this driver.
The people from OnStream, especially Jack Bombeeck did support this project
and always tried to answer HW or FW related questions. Furthermore, he
pushed the FW developers to do the right things.
SuSE did support this project by allowing me to work on it during my working
time for them and by integrating the driver into their distro.

More people did help by sending useful comments. Sorry to those who have
been forgotten. Thanks to all the GNU/FSF and Linux developers who made this
platform such an interesting, nice and stable platform.
Thanks go to those who tested the drivers and did send useful reports. Your
help is needed!


Makedevs.sh
-----------
#!/bin/sh
# Script to create OnStream SC-x0 device nodes (major 206)
# Usage: Makedevs.sh [nos [path to dev]]
# $Id: README.osst.kernel,v 1.4 2000/12/20 14:13:15 garloff Exp $
major=206
nrs=4
dir=/dev
test -z "$1" || nrs=$1
test -z "$2" || dir=$2
declare -i nr
nr=0
test -d $dir || mkdir -p $dir
while test $nr -lt $nrs; do
  mknod $dir/osst$nr c $major $nr
  chown 0.disk $dir/osst$nr; chmod 660 $dir/osst$nr;
  mknod $dir/nosst$nr c $major $[nr+128]
  chown 0.disk $dir/nosst$nr; chmod 660 $dir/nosst$nr;
  mknod $dir/osst${nr}l c $major $[nr+32]
  chown 0.disk $dir/osst${nr}l; chmod 660 $dir/osst${nr}l;
  mknod $dir/nosst${nr}l c $major $[nr+160]
  chown 0.disk $dir/nosst${nr}l; chmod 660 $dir/nosst${nr}l;
  mknod $dir/osst${nr}m c $major $[nr+64]
  chown 0.disk $dir/osst${nr}m; chmod 660 $dir/osst${nr}m;
  mknod $dir/nosst${nr}m c $major $[nr+192]
  chown 0.disk $dir/nosst${nr}m; chmod 660 $dir/nosst${nr}m;
  mknod $dir/osst${nr}a c $major $[nr+96]
  chown 0.disk $dir/osst${nr}a; chmod 660 $dir/osst${nr}a;
  mknod $dir/nosst${nr}a c $major $[nr+224]
  chown 0.disk $dir/nosst${nr}a; chmod 660 $dir/nosst${nr}a;
  let nr+=1
done