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passthrough devices vs. named devices

 
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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 HPUX

st

st(1M)																	    st(1M)

NAME

       st - shared tape administration

SYNOPSIS

       device_file

DESCRIPTION

       The  command  provides  users  with a command-line interface to check the status of a shared tape device or to reclaim a shared tape device
       from a host system that has failed while holding a reservation on the shared tape device.  The command can also be used for the	same  pur-
       pose on shared library robotic devices.	To use the command you must have root user id.

       Please see examples below for usage.

   Options
       recognizes the following options and arguments:

       Specifies the tape device file or sctl/esctl pass-through device
		      file for the shared tape/library device. This parameter is mandatory and will report an error if device_file is omitted.

       Allows the user to reclaim a shared tape device or shared
		      library robotic device in the case where a host failed while holding a reservation on the shared device.	This option causes
		      a bus device reset to be issued to the device specified by the option.

       Prints out the current status of the shared tape/library
		      device specified by the option.

RETURN VALUE

       returns 0 upon successful completion and 1 otherwise.

EXAMPLES

       The following shows three examples of output from the above command.

       The above output indicates that the shared device is reserved by another host and is therefore unavailable at this time.

       The above output indicates that the shared device is not ready for use at this time.

       The above output indicates that the shared device is ready for use at this time.

       To reclaim a shared tape/library device from a failed host, the following command can be used:

WARNINGS

       The option must be used with care. When reclaiming devices, it must be ensured that the host from which the device is being  reclaimed  has
       in fact failed, as data may be lost as the result of reclaiming a device that is currently in use by another host.

AUTHOR

       was developed by Hewlett-Packard.

SEE ALSO

       mt(1), scsi(7), scsi_ctl(7).

																	    st(1M)