<< Back to man.ChinaUnix.net

Chapter 9. chg-scsi

Jason X (report real name to )

Original version

Stefan G. Weichinger

AMANDA Core Team

Table of Contents

Command line options
Notes about changer.conf
Amanda's actual usage of chg-scsi
Configuration notes
Hacking notes


Refer to http://www.amanda.org/docs/chgscsi.html for the current version of this document.

Jason's new and improved chg-scsi documentation.

This documentation will also include an occasional reference to the mtx suite as I have attempted to use chg-zd-mtx. I use mtx often as a fast query tool. Please also refer to Amanda Tape Changer Support for additional details.

My equipment list is as follows:

  • Redhat 7.0 machine

    • Dual Processor P-III

    • Sony DDS3 tape drive

    • lots of hard disk space

  • Quantum/ATL L500 SCSI changer

  • DLT tape drive (three possible)

  • barcode reader fourteen tape slots

I base this documentation on the following:

  • mtx version 1.2.16rel

  • Amanda version 2.4.3b3

  • SCSI2 specification: X3T9.2/375R revision 10L

  • Quantum/ATL Field Service Manual 6321101-03 Ver.3, rel.0

  • Quantum DLT800 Tape system product manual 02 April, 2001 81-60118-04

  • the SCSI bus and IDE interface 2nd ed by Friedhelm Schmidt pub: Addison-Wesley 1998

Note that Quantum/ATL's L-series changers follow the SCSI command set, and do not use any proprietary commands. Thus, it was fairly simple to make this work.

I had to install Amanda --with-suffixes and setup my server's client side of things using Amanda-2.4.2p2 --with-suffixes.

Please note that my usage of "barcode" and "barcode reader" throughout this document really refers to "physical tape identification system". for example: the EEPROM in the AIT cartridge.

Command line options

chg-scsi's command line options:

-slot <param>
-label <param>
-search <param>
-status <param>
-trace <param>

Note that chg-scsi is called by Amanda in the context of whatever Amanda configuration Amanda is currently using. In short, to call chg-scsi by hand, change to your Amanda configuration directory, then run chg-scsi.

-slot <param> command:

this command takes either a slot number, or any one of the following: current, next, prev, first, last, advance

It then loads the appropriate tape into the drive.

Note that if the tape is already loaded, no changer motion will happen. No reading of the tape is done here.

-info command:

four numbers are printed: <slot# loaded> <number of slots> <reversable> <searchable>

with chg-scsi, the reversable number is always 1. Searchable is set based on if a barcode reader is available and working correctly.

-reset command:

Tape is unloaded, and slot 0 is loaded. No actual reset command is sent to the changer.

-eject command:

Tape is unloaded, and put back into its original slot.

-clean command:

Cleaning tape (if configured) is loaded into the tape. It is probably unloaded when done. I haven't looked closely at this yet.

-label <param> command:

This appears to take the currently loaded tape's barcode and write it to the labelfile with the given parameter as it's tape header. I have not tested this.

-search <param> command:

this only should be used if a barcode reader is present, or emulate barcode is turned on.

the required parameter is an Amanda tape label. The label searched in the labelfile. If a barcode is found, then that tape is loaded directly.

I believe the fallback is to search the entire magazine.

-status command:

The tape changer is queried, and the results are printed out. Values printed are what slots exist, are they full or empty, and what volume labels (barcodes) they are.

Q. what about changers that don't retain current slot? A. this is what the "statfile" is for.

-trace command:

present only for a particular type of changer.

-inventory: (this takes a LONG time to do)

unloads tape back to its slot issues command to changer to do an inventory of itself (read all barcodes...)

loads each tape, retrieves the barcode, and reads the Amanda

label off of the tape itself stores/updates the label database file


prints out in human readable form the label database contents from the labelfile.

-scan: (aka scanbus)

scans the SCSI generic interfaces (eg: linux sg), and prints out the device name and the device types. I found that linux didn't classify either of my tape devices as generic, but this facility did.

USE THIS FOR FINDING VALUE OF SCSItapedev. Be certain though you have the correct tape drive: I came close to wreaking havoc with my DDS3 drive while it was flushing Amanda data...and my changer has a DLT drive! Please refer to my configuration notes below.


prints out a SAMPLE changer.conf file. Note that I said sample. except for that it also does a scanbus. if you have more than one tape drive, please be certain it is correct as chg-scsi uses the first one it finds.

Please refer to my configuration notes below.

Notes about changer.conf

Here, I try to be a bit more clear on what these config values mean.

"number_configs" MUST be the first entry (not counting comments)

"emubarcode" will set this value in chg-scsi regardless of the value you try to assign it. If you don't want "emubarcode" set, don't list it!

"havebarcode" have barcode is tempered by what devices chg-scsi is aware of. if chg-scsi doesn't know about your changer explicitly, it will default to a default changer. the default changer has no barcode reader.

In a patch I plan to post, I have added a generic changer that does use a barcode. set "changerident" to "genericbarcode" to use this.

"sleep" number of seconds for chg-scsi to wait for a "tape drive ready" command after loading a new tape. Mine is 140 as I have a DLT tape drive, and my tape drive manual reports a max of 133 seconds to be ready.

"config" this is a header telling chg-scsi that all values following, up to the next "config" line apply to this drive number. It is this number that is refered to in your amanda.conf file as line tapedev

"drivenum" this is the tape drive number in your changer. For a single tape drive, this is zero. Mine can handle up to three, so I expect I could make this 0, 1, or 2.

"dev" the SCSI device of your tape drive. under linux, in my case it is /dev/nst1. This MUST be defined.

"SCSItapedev" The generic SCSI device of your tape drive. this is simply the generic interface to the device "dev" above. This entry is optional. In my case, it is /dev/sg2. If this entry exists and is legitimate, then SCSI commands are formed directly instead of using ioctl commands.

"startuse" "enduse" The start and end slots of your changer. Note that these also start with zero.

"eject" chg-scsi tells the tape changer to eject. You might need to explicitly tell the tape drive to unload first. That's what this setting is for. Have you ever removed a loaded VCR tape by hand?

"changerident" chg-scsi will first read the changer's identification from the return of the SCSI "inquiry" command. If changerident is set in the configuration file, the SCSI inquiry's value is overridden. chg-scsi will attempt to match the value with its built-in changertypes.

"generic" is what the chg-scsi will default to "genericbarcode" is a hack of mine that forces the changer's barcode reader to work. Note that if your changer uses a superset of the SCSI command set, this probably won't work. "L500" is another addition of mine that will enable a quantum/atl L500 to work correctly. It might even work with an L200.

other values are (taken from the code)

  • C1553A (HP Auto Loader)

  • EXB-10e, EXB-120 (Exabyte Robot)

  • EXB-85058HE-0000 (Exabyte Tape)

  • TDS 1420 (Tandberg Robot)


  • FastStor DLT (ADIC FastStor DLT Library)

  • Scalar DLT 448 (ADIC DLT 448)

  • 215 (Spectra Logic TreeFrog)

  • Quad 7 (Breece Hill)

  • DLT7000, DLT4000 (DLT Tape)

"debuglevel" setting this to "9:0" is very informative.

"statfile" stores which "slot" that the tape in the drive came from

"labelfile" binary file that stores the tape header and barcode information

cleanmax cleancart cleanfile I have my changer set to autoclean, and the slot the cleaning cartridge is in is not available for any other use.

Amanda's actual usage of chg-scsi

this should be brief: Amanda really only issues "slot next" type commands. Currently Amanda doesn't ask chg-scsi to load "tape x with label Daily_set023". the chg-scsi mechanism is there for use, and functions quite well for the user to load a particular tape. I understand they (the Amanda team) are working on this.

Configuration notes

(assuming one changer with one tape drive!)

in amanda.conf:

set tpchanger to chg-scsi set changerfile to <pathname>/changer.conf set tapedev to 0 set changerdev to /dev/<changer generic device>

  • this value is usually listed in the system boot messages or will be printed via syslog when the appropriate kernel module is loaded. eg: linux modprobe sg

in changer.conf: set number_configs to 1 set dev to <non-rewinding tape device eg: /dev/nst1> set debug to 9:0

run "chg-scsi -scan" from your Amanda configuration directory I get: name /dev/sg0 Tape Count 1 name /dev/sg1 Changer Count 2 name /dev/sg2 Tape Count 3

I set SCSItapedev to /dev/sg0 to test with, then ran chg-scsi -info. Check the chg-scsi debug file for tapeidentification details. This is where I discoverd that "sg0" was not the correct tape!

set SCSItapedev to "/dev/<generic device>"

if you have no barcode, try "changerident generic" if you have a barcode reader try "changerident genericbarcode"

Hacking notes

My hacks are:

  • adding printout of "emubarcode" values in the debug file

  • added dlt8000 tape drive to ChangerIO[], and SenseType[]

  • added genericbarcode to ChangerIO[], and SenseType[]

  • added L500 to ChangerIO[], and SenseType[]

  • added a couple of basic sensecodes listed in the SCSI specs for the generic and genericbarcode tape changers.

My desires are:

  • modify the sensecode code such that all SCSI devices inherit the standard SCSI codes and may override or append to them as needed.

  • modify the configuration reading code and the inquiry command to allow spaces. eg: my changer displays the following ident data: "L500 6320000" but I had to create a type called "L500" or else the spaces would throw off the comparisons.