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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>
<UL>
<LI><A NAME="tex2html1735"
HREF="Autochanger_Support.html#SECTION003110000000000000000">Knowing What SCSI Devices You Have</A>
<LI><A NAME="tex2html1736"
HREF="Autochanger_Support.html#SECTION003120000000000000000">Example Scripts</A>
<LI><A NAME="tex2html1737"
HREF="Autochanger_Support.html#SECTION003130000000000000000">Slots</A>
<LI><A NAME="tex2html1738"
HREF="Autochanger_Support.html#SECTION003140000000000000000">Multiple Devices</A>
<LI><A NAME="tex2html1739"
HREF="Autochanger_Support.html#SECTION003150000000000000000">Device Configuration Records</A>
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<H1><A NAME="SECTION003100000000000000000"></A>
<A NAME="AutochangersChapter"></A>
<BR>
Autochanger Support
</H1>
<A NAME="16687"></A>
<A NAME="16688"></A>
<P>
Bacula provides autochanger support for reading and writing tapes. In
order to work with an autochanger, Bacula requires a number of things, each of
which is explained in more detail after this list:
<P>
<UL>
<LI>A script that actually controls the autochanger according to commands
sent by Bacula. We furnish such a script that works with <B>mtx</B> found in
the <B>depkgs</B> distribution.
<P>
</LI>
<LI>That each Volume (tape) to be used must be defined in the Catalog and
have a Slot number assigned to it so that Bacula knows where the Volume is
in the autochanger. This is generally done with the <B>label</B> command, but
can also done after the tape is labeled using the <B>update slots</B>
command. See below for more details. You must pre-label the tapes manually
before using them.
<P>
</LI>
<LI>Modifications to your Storage daemon's Device configuration resource to
identify that the device is a changer, as well as a few other parameters.
<P>
</LI>
<LI>You should also modify your Storage resource definition in the
Director's configuration file so that you are automatically prompted for the
Slot when labeling a Volume.
<P>
</LI>
<LI>You need to ensure that your Storage daemon (if not running as root)
has access permissions to both the tape drive and the control device.
<P>
</LI>
<LI>You need to have <B>Autochanger = yes</B> in your Storage resource
in your bacula-dir.conf file so that you will be prompted for the
slot number when you label Volumes.
</LI>
</UL>
<P>
In version 1.37 and later, there is a new Autochanger
resourceAutochangerRes that permits you to group Device resources thus
creating a multi-drive autochanger. If you have an autochanger,
you <B>must</B> use this new resource.
<P>
Bacula uses its own <B>mtx-changer</B> script to interface with a program
that actually does the tape changing. Thus in principle, <B>mtx-changer</B>
can be adapted to function with any autochanger program, or you can
call any other script or program. The current
version of <B>mtx-changer</B> works with the <B>mtx</B> program. However,
FreeBSD users have provided a script in the <B>examples/autochangers</B>
directory that allows Bacula to use the <B>chio</B> program.
<P>
Bacula also supports autochangers with barcode
readers. This support includes two Console commands: <B>label barcodes</B>
and <B>update slots</B>. For more details on these commands, see the "Barcode
Support" section below.
<P>
Current Bacula autochanger support does not include cleaning, stackers, or
silos. Stackers and silos are not supported because Bacula expects to
be able to access the Slots randomly.
However, if you are very careful to setup Bacula to access the Volumes
in the autochanger sequentially, you may be able to make Bacula
work with stackers (gravity feed and such).
<P>
Support for multi-drive
autochangers requires the Autochanger resourceAutochangerRes
introduced in version 1.37. This resource is also recommended for single
drive autochangers.
<P>
In principle, if <B>mtx</B> will operate your changer correctly, then it is
just a question of adapting the <B>mtx-changer</B> script (or selecting one
already adapted) for proper interfacing. You can find a list of autochangers
supported by <B>mtx</B> at the following link:
http://mtx.opensource-sw.net/compatibility.php
http://mtx.opensource-sw.net/compatibility.php.
The home page for the <B>mtx</B> project can be found at:
http://mtx.opensource-sw.net/http://mtx.opensource-sw.net/.
<P>
Note, we have feedback from some users that there are certain
incompatibilities between the Linux kernel and mtx. For example between
kernel 2.6.18-8.1.8.el5 of CentOS and RedHat and version 1.3.10 and 1.3.11
of mtx. This was fixed by upgrading to a version 2.6.22 kernel.
<P>
In addition, apparently certain versions of mtx, for example, version
1.3.11 limit the number of slots to a maximum of 64. The solution was to
use version 1.3.10.
<P>
If you are having troubles, please use the <B>auto</B> command in the <B>btape</B> program to test the functioning of your autochanger with Bacula. When
Bacula is running, please remember that for many distributions (e.g. FreeBSD,
Debian, ...) the Storage daemon runs as <B>bacula.tape</B> rather than <B>root.root</B>, so you will need to ensure that the Storage daemon has sufficient
permissions to access the autochanger.
<P>
Some users have reported that the the Storage daemon blocks under certain
circumstances in trying to mount a volume on a drive that has a different
volume loaded. As best we can determine, this is simply a matter of
waiting a bit. The drive was previously in use writing a Volume, and
sometimes the drive will remain BLOCKED for a good deal of time (up to 7
minutes on a slow drive) waiting for the cassette to rewind and to unload
before the drive can be used with a different Volume.
<P>
<A NAME="SCSI_devices"></A>
<H1><A NAME="SECTION003110000000000000000">
Knowing What SCSI Devices You Have</A>
</H1>
<A NAME="16723"></A>
<A NAME="16724"></A>
<A NAME="16725"></A>
<A NAME="16726"></A>
<P>
Under Linux, you can
<P>
<PRE>
cat /proc/scsi/scsi
</PRE>
<P>
to see what SCSI devices you have available. You can also:
<P>
<PRE>
cat /proc/scsi/sg/device_hdr /proc/scsi/sg/devices
</PRE>
<P>
to find out how to specify their control address (<B>/dev/sg0</B> for the
first, <B>/dev/sg1</B> for the second, ...) on the <B>Changer Device = </B>
Bacula directive.
<P>
You can also use the excellent <B>lsscsi</B> tool.
<PRE>
$ lsscsi -g
[1:0:2:0] tape SEAGATE ULTRIUM06242-XXX 1619 /dev/st0 /dev/sg9
[1:0:14:0] mediumx STK L180 0315 /dev/sch0 /dev/sg10
[2:0:3:0] tape HP Ultrium 3-SCSI G24S /dev/st1 /dev/sg11
[3:0:0:0] enclosu HP A6255A HP04 - /dev/sg3
[3:0:1:0] disk HP 36.4G ST336753FC HP00 /dev/sdd /dev/sg4
</PRE>
<P>
For more detailed information on what SCSI devices you have please see
the Linux SCSI TricksSCSITricks section of the Tape Testing
chapter of this manual.
<P>
Under FreeBSD, you can use:
<P>
<PRE>
camcontrol devlist
</PRE>
<P>
To list the SCSI devices as well as the <B>/dev/passn</B> that you will use on
the Bacula <B>Changer Device = </B> directive.
<P>
Please check that your Storage daemon has permission to access this
device.
<P>
The following tip for FreeBSD users comes from Danny Butroyd:
on reboot Bacula will NOT have permission to
control the device /dev/pass0 (assuming this is your changer device).
To get around this just edit the /etc/devfs.conf file and add the
following to the bottom:
<PRE>
own pass0 root:bacula
perm pass0 0666
own nsa0.0 root:bacula
perm nsa0.0 0666
</PRE>
<P>
This gives the bacula group permission to write to the nsa0.0 device
too just to be on the safe side. To bring these changes into effect
just run:-
<P>
/etc/rc.d/devfs restart
<P>
Basically this will stop you having to manually change permissions on these
devices to make Bacula work when operating the AutoChanger after a reboot.
<P>
<A NAME="scripts"></A>
<H1><A NAME="SECTION003120000000000000000">
Example Scripts</A>
</H1>
<A NAME="16747"></A>
<A NAME="16748"></A>
<P>
Please read the sections below so that you understand how autochangers work
with Bacula. Although we supply a default <B>mtx-changer</B> script, your
autochanger may require some additional changes. If you want to see examples
of configuration files and scripts, please look in the <B>bacula-src/examples/devices</B> directory where you will find an
example <B>HP-autoloader.conf</B> Bacula Device resource, and several <B>mtx-changer</B> scripts that have been modified to work with different
autochangers.
<P>
<A NAME="Slots"></A>
<P>
<H1><A NAME="SECTION003130000000000000000">
Slots</A>
</H1>
<A NAME="16756"></A>
<P>
To properly address autochangers, Bacula must know which Volume is in each
<B>slot</B> of the autochanger. Slots are where the changer cartridges reside
when not loaded into the drive. Bacula numbers these slots from one to the
number of cartridges contained in the autochanger.
<P>
Bacula will not automatically use a Volume in your autochanger unless it is
labeled and the slot number is stored in the catalog and the Volume is marked
as InChanger. This is because it must know where each volume is (slot) to
be able to load the volume.
For each Volume in your
changer, you will, using the Console program, assign a slot. This information
is kept in <B>Bacula's</B> catalog database along with the other data for the
volume. If no slot is given, or the slot is set to zero, Bacula will not
attempt to use the autochanger even if all the necessary configuration records
are present. When doing a <B>mount</B> command on an autochanger, you must
specify which slot you want mounted. If the drive is loaded with a tape
from another slot, it will unload it and load the correct tape, but
normally, no tape will be loaded because an <B>unmount</B> command causes
Bacula to unload the tape in the drive.
<P>
You can check if the Slot number and InChanger flag are set by doing a:
<PRE>
list Volumes
</PRE>
<P>
in the Console program.
<P>
<A NAME="mult"></A>
<H1><A NAME="SECTION003140000000000000000">
Multiple Devices</A>
</H1>
<A NAME="16765"></A>
<A NAME="16766"></A>
<P>
Some autochangers have more than one read/write device (drive). The
new Autochanger resourceAutochangerRes introduced in version
1.37 permits you to group Device resources, where each device
represents a drive. The Director may still reference the Devices (drives)
directly, but doing so, bypasses the proper functioning of the
drives together. Instead, the Director (in the Storage resource)
should reference the Autochanger resource name. Doing so permits
the Storage daemon to ensure that only one drive uses the mtx-changer
script at a time, and also that two drives don't reference the
same Volume.
<P>
Multi-drive requires the use of the <B>Drive Index</B> directive in the Device resource of the Storage daemon's
configuration file. Drive numbers or the Device Index are numbered beginning
at zero, which is the default. To use the second Drive in an autochanger, you
need to define a second Device resource and set the Drive Index to 1 for
that device. In general, the second device will have the same <B>Changer
Device</B> (control channel) as the first drive, but a different <B>Archive
Device</B>.
<P>
As a default, Bacula jobs will prefer to write to a Volume that is
already mounted. If you have a multiple drive autochanger and you want
Bacula to write to more than one Volume in the same Pool at the same
time, you will need to set Prefer Mounted Volumes PreferMountedVolumes
in the Directors Job resource to <B>no</B>. This will cause
the Storage daemon to maximize the use of drives.
<P>
<A NAME="ConfigRecords"></A>
<H1><A NAME="SECTION003150000000000000000">
Device Configuration Records</A>
</H1>
<A NAME="16777"></A>
<A NAME="16778"></A>
<P>
Configuration of autochangers within Bacula is done in the Device resource of
the Storage daemon. Four records: <B>Autochanger</B>, <B>Changer Device</B>,
<B>Changer Command</B>, and <B>Maximum Changer Wait</B> control how Bacula uses
the autochanger.
<P>
These four records, permitted in <B>Device</B> resources, are described in
detail below. Note, however, that the <B>Changer Device</B> and the
<B>Changer Command</B> directives are not needed in the Device resource
if they are present in the <B>Autochanger</B> resource.
<P>
<DL>
<DT><STRONG>Autochanger = <I>Yes|No</I> </STRONG></DT>
<DD><A NAME="16789"></A>
The <B>Autochanger</B> record specifies that the current device is or is not
an autochanger. The default is <B>no</B>.
<P>
</DD>
<DT><STRONG>Changer Device = device-name</STRONG></DT>
<DD><A NAME="16794"></A>
In addition to the Archive Device name, you must specify a <B>Changer
Device</B> name. This is because most autochangers are controlled through a
different device than is used for reading and writing the cartridges. For
example, on Linux, one normally uses the generic SCSI interface for
controlling the autochanger, but the standard SCSI interface for reading and
writing the tapes. On Linux, for the <B>Archive Device = /dev/nst0</B>, you
would typically have <B>Changer Device = /dev/sg0</B>. Note, some of the more
advanced autochangers will locate the changer device on <B>/dev/sg1</B>. Such
devices typically have several drives and a large number of tapes.
<P>
On FreeBSD systems, the changer device will typically be on <B>/dev/pass0</B>
through <B>/dev/passn</B>.
<P>
On Solaris, the changer device will typically be some file under <B>/dev/rdsk</B>.
<P>
Please ensure that your Storage daemon has permission to access this
device.
<P>
</DD>
<DT><STRONG>Changer Command = command</STRONG></DT>
<DD><A NAME="16804"></A>
This record is used to specify the external program to call and what
arguments to pass to it. The command is assumed to be a standard program or
shell script that can be executed by the operating system. This command is
invoked each time that Bacula wishes to manipulate the autochanger. The
following substitutions are made in the <B>command</B> before it is sent to
the operating system for execution:
<P>
<PRE>
%% = %
%a = archive device name
%c = changer device name
%d = changer drive index base 0
%f = Client's name
%j = Job name
%o = command (loaded, load, or unload)
%s = Slot base 0
%S = Slot base 1
%v = Volume name
</PRE>
<P>
An actual example for using <B>mtx</B> with the <B>mtx-changer</B> script (part
of the Bacula distribution) is:
<P>
<PRE>
Changer Command = "/etc/bacula/mtx-changer %c %o %S %a %d"
</PRE>
<P>
Where you will need to adapt the <B>/etc/bacula</B> to be the actual path on
your system where the mtx-changer script resides. Details of the three
commands currently used by Bacula (loaded, load, unload) as well as the
output expected by Bacula are give in the <B>Bacula Autochanger Interface</B>
section below.
<P>
</DD>
<DT><STRONG>Maximum Changer Wait = time</STRONG></DT>
<DD><A NAME="16816"></A>
This record is used to define the maximum amount of time that Bacula
will wait for an autoloader to respond to a command (e.g. load). The
default is set to 120 seconds. If you have a slow autoloader you may
want to set it longer.
<P>
If the autoloader program fails to respond in this time, it will be killed
and Bacula will request operator intervention.
<P>
</DD>
<DT><STRONG>Drive Index = number</STRONG></DT>
<DD><A NAME="16819"></A>
This record allows you to tell Bacula to use the second or subsequent
drive in an autochanger with multiple drives. Since the drives are
numbered from zero, the second drive is defined by
<P>
<PRE>
Device Index = 1
</PRE>
<P>
To use the second drive, you need a second Device resource definition in the
Bacula configuration file. See the Multiple Drive section above in this
chapter for more information.
</DD>
</DL>
<P>
In addition, for proper functioning of the Autochanger, you must
define an Autochanger resource.
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