[2493] in linux-scsi channel archive
Re: SCSI Tape driver
daemon@ATHENA.MIT.EDU (Kai M{kisara)
Thu Sep 18 17:38:42 1997
Date: Thu, 18 Sep 1997 23:41:30 +0300 (EET DST)
From: Kai M{kisara <makisara@abies.metla.fi>
Reply-To: Kai.Makisara@metla.fi
To: Michael Stone <mstone@itri.loyola.edu>
cc: root@chaos.analogic.com, linux-scsi@vger.rutgers.edu
In-Reply-To: <19970918110955.19881@beijing.itri.loyola.edu>
Re-routed to linux-scsi where this belongs.
On Thu, 18 Sep 1997, Michael Stone wrote:
> Quoting Richard B. Johnson (root@chaos.analogic.com):
> > The SCSI tape devices have a major and minor number. If you want the tape
...
> > if supported unload, you use /dev/st0.
>
> Hmm. In my copy of devices.txt, it says this:
>
> 9 char SCSI tape devices
> 0 = /dev/st0 First SCSI tape, mode 0
> 1 = /dev/st1 Second SCSI tape, mode 0
> ...
> 32 = /dev/st0l First SCSI tape, mode 1
> 33 = /dev/st1l Second SCSI tape, mode 1
> ...
...
>
> As long as I'm sending stuff off to the list, can someone answer another
> question: What do the postfixes l, m, and a mean? (IOW, what are the
> 4 modes for tapes?)
>
The modes are explained in linux/drivers/scsi/README.st but here is a
brief explanation (I guess very few people have actually used the modes so
far):
Firstly, the device names don't matter, only the major and minor numbers.
The names for devices.txt have been selected to resemble the names
commonly used in other Unices.
Originally st only had two minors for each drive: the auto-rewind and the
non-rewind device. The block size and other characteristics were then set
with mt. This is still the default operation but since 2.0.0 the user has
had the possibility to define up to four (* 2) different devices for each
drive and each device can have different characteristics (block size,
compression, etc.). There were two reasons for making this possible:
1. The other unices have devices with different characteristics for
the same drive.
2. Letting a user freely change the drive parameters is not very nice in a
multiuser environment (the next user has to set all parameters
in order to be sure that the drive operates correctly). It is better
if the system administrator defines the possible alternatives. (Even if
the modes are defined, the user can change the parameters but the
driver restores them when a new tape is loaded.)
When the system starts, only the first mode is active. Other modes for a
drive become active when the superuser defines the characteristics. This
can be done with mt but there will be more user-friendly (?) tools in near
future.
Kai
