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Full Discussion: passthrough devices vs. named devices
Top Forums UNIX for Dummies Questions & Answers passthrough devices vs. named devices Post 302202331 by thumper on Wednesday 4th of June 2008 02:41:35 PM
Old 06-04-2008
passthrough devices vs. named devices
I am having trouble understanding the difference between a passthrough device and a named device and when you would use one or the other to access equipment.

As an example, we have a tape library and giving the command
"camcontrol devlist" gives the following output:

akx[22]# camcontrol devlist
<SPECTRA 215 1014> at scbus3 target 3 lun 0 (pass4,ch0)
<SONY SDX-300C 04c7> at scbus3 target 8 lun 0 (pass5,sa0)

The SPECTRA 215 is the tape library the SONY SDX is the tape drive in the library.
To address the tape library a command such as "mtx -f /dev/pass4 command" is used, however to address the tape unit then /dev/sa0 would be used as in
"/sbin/dump -0uaf /dev/sa0 /dev/da4s1e".

Could someone give me a clue on when you address a passthrough device and when you address a named device, or at point me to some documentation that might clear this up?

Thanks
Thumper
 

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LEARN ABOUT CENTOS

scsieject

scsieject(1)						      General Commands Manual						      scsieject(1)

NAME

       scsieject - control SCSI tape devices

SYNOPSIS

       scsieject [-f <scsi-generic-device>] commands

DESCRIPTION

       The scsieject command controls SCSI devices in a platform-independent manner. As long as 'mtx' works on the platform, so does 'scsieject'.

OPTIONS

       The first argument, given following -f , is the SCSI generic device corresponding to your tape drive.  Consult your operating system's doc-
       umentation for more information (for example, under Linux  these  are  generally  /dev/sg0  through  /dev/sg15,	under  FreeBSD	these  are
       /dev/pass0  through  /dev/passX.  Under Solaris this is usually the same as your tape drive (Solaris has a SCSI passthrough ioctl). You can
       set the STAPE or TAPE environment variable rather than use -f.

COMMANDS

       load	 Load the medium into the drive.  When this command is issued to a CD/DVD drive  and  the  tray  is  extended  the  tray  will	be
		 retracted if the drive is capable of it.

       unload	 Unload  the medium from the drive (also known as eject).  When this command is issued to a CD/DVD drive or a tape drive the media
		 will be ejected if the device supports it.

       start	 Start the device.  Some devices require a start command after a media changer has loaded new media into the device.

       stop	 Stop the device.  Some devices require a stop command prior to unloading the medium from the device when using a media changer.

       lock	 Lock the device.  Locks the device so that the medium cannot be removed manually.

       unlock	 Unlock the device.  Unlocks the device so that the medium can be removed manually.

AUTHORS

       This program was written by Robert Nelson <robertnelson@users.sourceforge.net> based on the scsitape program  written  by  Eric	Lee  Green
       <eric@badtux.org>.  Major portions of the 'mtxl.c' library used herein were written by Leonard Zubkoff.

HINTS

       Under  Linux,  cat /proc/scsi/scsi will tell you what SCSI devices you have.  You can then refer to them as /dev/sga, /dev/sgb, etc. by the
       order they are reported.

       Under FreeBSD, camcontrol devlist will tell you what SCSI devices you have, along with which pass device controls them.

       Under Solaris 7 and 8, /usr/sbin/devfsadm -C will clean up your /devices directory. Then find /devices -name 'st@*' -print  will  return  a
       list of all tape drives. /dev on Solaris is apparently only of historical interest.

BUGS AND LIMITATIONS

       There are no known bugs or limitations.

AVAILABILITY

       This version of scsieject is currently being maintained by Robert Nelson <robertnelson@users.sourceforge.net> as part of the 'mtx' suite of
       programs. The 'mtx' home page  is  http://mtx.sourceforge.net  and  the	actual	code  is  currently  available	there  and  via  SVN  from
       http://sourceforge.net/projects/mtx.

SEE ALSO

       loaderinfo(1),tapeinfo(1),mtx(1)

								   scsieject1.0 						      scsieject(1)
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