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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 REDHAT

tapeinfo

TAPEINFO(1)						      General Commands Manual						       TAPEINFO(1)

NAME

       tapeinfo - report SCSI tape device info

SYNOPSIS

       tapeinfo -f <scsi-generic-device>

DESCRIPTION

       The  tapeinfo  command  reads  various information from SCSI tape drives that is not generally available via most vendors' tape drivers. It
       issues raw commands directly to the tape drive, using either the  operating  system's  SCSI  generic  device  (	e.g.  /dev/sg0	on  Linux,
       /dev/pass0 on FreeBSD) or the raw SCSI I/O ioctl on a tape device on some operating systems.

       One  good  time	to  use 'tapeinfo' is immediately after a tape i/o operation has failed. On tape drives that support HP's 'tapealert' API,
       'tapeinfo' will report a more exact description of what went wrong.

       Do be aware that 'tapeinfo' is not a substitute for your operating system's own 'mt' or similar tape driver control program. It is intended
       to supplement, not replace, programs like 'mt' that access your operating system's tape driver in order to report or set information.

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 start at /dev/sg0 under FreeBSD these start at /dev/pass0).

       Under FreeBSD, 'camcontrol devlist' will tell you what SCSI devices you have, along with which 'pass' device controls  them.  Under  Linux,
       "cat /proc/scsi/scsi" will tell you what SCSI devices you have.

BUGS AND LIMITATIONS

       This program has only been tested on Linux with a limited number of tape drives (HP DDS4, Seagate AIT).

AVAILABILITY

       tapeinfo  is  currently being maintained by Eric Lee Green <eric@badtux.org> formerly of Enhanced Software Technologies Inc. The 'mtx' home
       page is http://mtx.sourceforge.net and the actual code is currently available there and via CVS from http://sourceforge.net/projects/mtx/ .

SEE ALSO

       mt(1),mtx(1),scsitape(1)

								    TAPEINFO1.0 						       TAPEINFO(1)
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