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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:
In version 1.37 and later, there is a new Autochanger resource that permits you to group Device resources thus creating a multi-drive autochanger. If you have an autochanger, you must use this new resource.
Bacula uses its own mtx-changer script to interface with a program that actually does the tape changing. Thus in principle, mtx-changer can be adapted to function with any autochanger program, or you can call any other script or program. The current version of mtx-changer works with the mtx program. However, FreeBSD users have provided a script in the examples/autochangers directory that allows Bacula to use the chio program.
Bacula also supports autochangers with barcode readers. This support includes two Console commands: label barcodes and update slots. For more details on these commands, see the "Barcode Support" section below.
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).
Support for multi-drive autochangers requires the Autochanger resource introduced in version 1.37. This resource is also recommended for single drive autochangers.
In principle, if mtx will operate your changer correctly, then it is just a question of adapting the mtx-changer script (or selecting one already adapted) for proper interfacing. You can find a list of autochangers supported by mtx at the following link: http://mtx.opensource-sw.net/compatibility.php. The home page for the mtx project can be found at: http://mtx.opensource-sw.net/.
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.
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.
If you are having troubles, please use the auto command in the btape 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 bacula.tape rather than root.root, so you will need to ensure that the Storage daemon has sufficient permissions to access the autochanger.
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.
Under Linux, you can
cat /proc/scsi/scsi
to see what SCSI devices you have available. You can also:
cat /proc/scsi/sg/device_hdr /proc/scsi/sg/devices
to find out how to specify their control address (/dev/sg0 for the first, /dev/sg1 for the second, ...) on the Changer Device = Bacula directive.
For more detailed information on what SCSI devices you have please see the Linux SCSI Tricks section of the Tape Testing chapter of this manual.
Under FreeBSD, you can use:
camcontrol devlist
To list the SCSI devices as well as the /dev/passn that you will use on the Bacula Changer Device = directive.
Please check that your Storage daemon has permission to access this device.
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:
own pass0 root:bacula perm pass0 0666 own nsa0.0 root:bacula perm nsa0.0 0666
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:-
/etc/rc.d/devfs restart
Basically this will stop you having to manually change permissions on these devices to make Bacula work when operating the AutoChanger after a reboot.
Please read the sections below so that you understand how autochangers work with Bacula. Although we supply a default mtx-changer script, your autochanger may require some additional changes. If you want to see examples of configuration files and scripts, please look in the <bacula-src>/examples/devices directory where you will find an example HP-autoloader.conf Bacula Device resource, and several mtx-changer scripts that have been modified to work with different autochangers.
To properly address autochangers, Bacula must know which Volume is in each slot 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.
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 Bacula's 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 mount 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 unmount command causes Bacula to unload the tape in the drive.
You can check if the Slot number and InChanger flag are set by doing a:
list Volumes
in the Console program.
Some autochangers have more than one read/write device (drive). The new Autochanger resource 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.
Multi-drive requires the use of the Drive Index 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 Changer Device (control channel) as the first drive, but a different Archive Device.
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 in the Directors Job resource to no. This will cause the Storage daemon to maximize the use of drives.
Configuration of autochangers within Bacula is done in the Device resource of the Storage daemon. Four records: Autochanger, Changer Device, Changer Command, and Maximum Changer Wait control how Bacula uses the autochanger.
These four records, permitted in Device resources, are described in detail below. Note, however, that the Changer Device and the Changer Command directives are not needed in the Device resource if they are present in the Autochanger resource.
On FreeBSD systems, the changer device will typically be on /dev/pass0 through /dev/passn.
On Solaris, the changer device will typically be some file under /dev/rdsk.
Please ensure that your Storage daemon has permission to access this device.
%% = %
%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
An actual example for using mtx with the mtx-changer script (part of the Bacula distribution) is:
Changer Command = "/etc/bacula/mtx-changer %c %o %S %a %d"
Where you will need to adapt the /etc/bacula 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 Bacula Autochanger Interface section below.
If the autoloader program fails to respond in this time, it will be killed and Bacula will request operator intervention.
Device Index = 1
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.
In addition, for proper functioning of the Autochanger, you must define an Autochanger resource.
Kern Sibbald 2009-02-06